Following the guide for APT repositories on this site, after adding the sources list, I get the following after the 'apt-get update' command:
Hit:1
http://ppa.launchpad.net/ubuntu-pi-flavour-makers/ppa/ubuntu focal InRelease
Hit:2
http://ports.ubuntu.com/ubuntu-ports focal InRelease
Hit:3
http://ports.ubuntu.com/ubuntu-ports focal-security InRelease
Ign:4
https://apt.tvheadend.org/stable focal InRelease
Hit:5
http://ports.ubuntu.com/ubuntu-ports focal-updates InRelease
Ign:6
https://apt.tvheadend.org/unstable focal InRelease
Hit:7
https://apt.tvheadend.org/stable focal Release
Hit:8
https://apt.tvheadend.org/unstable focal Release
Reading package lists... Done
W: Target Packages (main/binary-arm64/Packages) is configured multiple times in /etc/apt/sources.list:4 and /etc/apt/sources.list.d/tvheadend.list:1
W: Target Packages (main/binary-all/Packages) is configured multiple times in /etc/apt/sources.list:4 and /etc/apt/sources.list.d/tvheadend.list:1
W: Target Translations (main/i18n/Translation-en_US) is configured multiple times in /etc/apt/sources.list:4 and /etc/apt/sources.list.d/tvheadend.list:1
W: Target Translations (main/i18n/Translation-en) is configured multiple times in /etc/apt/sources.list:4 and /etc/apt/sources.list.d/tvheadend.list:1
W: Target Translations (main/i18n/Translation-de) is configured multiple times in /etc/apt/sources.list:4 and /etc/apt/sources.list.d/tvheadend.list:1
W: Target CNF (main/cnf/Commands-arm64) is configured multiple times in /etc/apt/sources.list:4 and /etc/apt/sources.list.d/tvheadend.list:1
W: Target CNF (main/cnf/Commands-all) is configured multiple times in /etc/apt/sources.list:4 and /etc/apt/sources.list.d/tvheadend.list:1
W: Skipping acquire of configured file 'ubuntu/binary-arm64/Packages' as repository '
https://apt.tvheadend.org/stable focal InRelease' doesn't have the component 'ubuntu' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'ubuntu/i18n/Translation-en' as repository '
https://apt.tvheadend.org/stable focal InRelease' doesn't have the component 'ubuntu' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'ubuntu/i18n/Translation-de' as repository '
https://apt.tvheadend.org/stable focal InRelease' doesn't have the component 'ubuntu' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'ubuntu/i18n/Translation-en_US' as repository '
https://apt.tvheadend.org/stable focal InRelease' doesn't have the component 'ubuntu' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'ubuntu/cnf/Commands-arm64' as repository '
https://apt.tvheadend.org/stable focal InRelease' doesn't have the component 'ubuntu' (component misspelt in sources.list?)
N: Skipping acquire of configured file 'main/binary-arm64/Packages' as repository '
https://apt.tvheadend.org/stable focal InRelease' doesn't support architecture 'arm64'
W: Skipping acquire of configured file 'Focal/binary-arm64/Packages' as repository '
https://apt.tvheadend.org/stable focal InRelease' doesn't have the component 'Focal' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'Focal/i18n/Translation-en_US' as repository '
https://apt.tvheadend.org/stable focal InRelease' doesn't have the component 'Focal' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'Focal/i18n/Translation-de' as repository '
https://apt.tvheadend.org/stable focal InRelease' doesn't have the component 'Focal' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'Focal/i18n/Translation-en' as repository '
https://apt.tvheadend.org/stable focal InRelease' doesn't have the component 'Focal' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'Focal/cnf/Commands-arm64' as repository '
https://apt.tvheadend.org/stable focal InRelease' doesn't have the component 'Focal' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'focal/binary-arm64/Packages' as repository '
https://apt.tvheadend.org/stable focal InRelease' doesn't have the component 'focal' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'focal/i18n/Translation-de' as repository '
https://apt.tvheadend.org/stable focal InRelease' doesn't have the component 'focal' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'focal/i18n/Translation-en_US' as repository '
https://apt.tvheadend.org/stable focal InRelease' doesn't have the component 'focal' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'focal/i18n/Translation-en' as repository '
https://apt.tvheadend.org/stable focal InRelease' doesn't have the component 'focal' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'focal/cnf/Commands-arm64' as repository '
https://apt.tvheadend.org/stable focal InRelease' doesn't have the component 'focal' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'stable/binary-arm64/Packages' as repository '
https://apt.tvheadend.org/stable focal InRelease' doesn't have the component 'stable' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'stable/i18n/Translation-en_US' as repository '
https://apt.tvheadend.org/stable focal InRelease' doesn't have the component 'stable' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'stable/i18n/Translation-en' as repository '
https://apt.tvheadend.org/stable focal InRelease' doesn't have the component 'stable' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'stable/i18n/Translation-de' as repository '
https://apt.tvheadend.org/stable focal InRelease' doesn't have the component 'stable' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'stable/cnf/Commands-arm64' as repository '
https://apt.tvheadend.org/stable focal InRelease' doesn't have the component 'stable' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'fossa/binary-arm64/Packages' as repository '
https://apt.tvheadend.org/stable focal InRelease' doesn't have the component 'fossa' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'fossa/i18n/Translation-de' as repository '
https://apt.tvheadend.org/stable focal InRelease' doesn't have the component 'fossa' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'fossa/i18n/Translation-en' as repository '
https://apt.tvheadend.org/stable focal InRelease' doesn't have the component 'fossa' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'fossa/i18n/Translation-en_US' as repository '
https://apt.tvheadend.org/stable focal InRelease' doesn't have the component 'fossa' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'fossa/cnf/Commands-arm64' as repository '
https://apt.tvheadend.org/stable focal InRelease' doesn't have the component 'fossa' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'Fossa/binary-arm64/Packages' as repository '
https://apt.tvheadend.org/stable focal InRelease' doesn't have the component 'Fossa' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'Fossa/i18n/Translation-en_US' as repository '
https://apt.tvheadend.org/stable focal InRelease' doesn't have the component 'Fossa' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'Fossa/i18n/Translation-de' as repository '
https://apt.tvheadend.org/stable focal InRelease' doesn't have the component 'Fossa' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'Fossa/i18n/Translation-en' as repository '
https://apt.tvheadend.org/stable focal InRelease' doesn't have the component 'Fossa' (component misspelt in sources.list?)
W: Skipping acquire of configured file 'Fossa/cnf/Commands-arm64' as repository '
https://apt.tvheadend.org/stable focal InRelease' doesn't have the component 'Fossa' (component misspelt in sources.list?)
W: Target Packages (main/binary-arm64/Packages) is configured multiple times in /etc/apt/sources.list.d/tvheadend.list:2 and /etc/apt/sources.list.d/tvheadend.list:3
W: Target Packages (main/binary-all/Packages) is configured multiple times in /etc/apt/sources.list.d/tvheadend.list:2 and /etc/apt/sources.list.d/tvheadend.list:3
W: Target Translations (main/i18n/Translation-en_US) is configured multiple times in /etc/apt/sources.list.d/tvheadend.list:2 and /etc/apt/sources.list.d/tvheadend.list:3
W: Target Translations (main/i18n/Translation-en) is configured multiple times in /etc/apt/sources.list.d/tvheadend.list:2 and /etc/apt/sources.list.d/tvheadend.list:3
W: Target Translations (main/i18n/Translation-de) is configured multiple times in /etc/apt/sources.list.d/tvheadend.list:2 and /etc/apt/sources.list.d/tvheadend.list:3
W: Target CNF (main/cnf/Commands-arm64) is configured multiple times in /etc/apt/sources.list.d/tvheadend.list:2 and /etc/apt/sources.list.d/tvheadend.list:3
W: Target CNF (main/cnf/Commands-all) is configured multiple times in /etc/apt/sources.list.d/tvheadend.list:2 and /etc/apt/sources.list.d/tvheadend.list:3
N: Skipping acquire of configured file 'main/binary-arm64/Packages' as repository '
https://apt.tvheadend.org/unstable focal InRelease' doesn't support architecture 'arm64'
W: Target Packages (main/binary-arm64/Packages) is configured multiple times in /etc/apt/sources.list:4 and /etc/apt/sources.list.d/tvheadend.list:1
W: Target Packages (main/binary-all/Packages) is configured multiple times in /etc/apt/sources.list:4 and /etc/apt/sources.list.d/tvheadend.list:1
W: Target Translations (main/i18n/Translation-en_US) is configured multiple times in /etc/apt/sources.list:4 and /etc/apt/sources.list.d/tvheadend.list:1
W: Target Translations (main/i18n/Translation-en) is configured multiple times in /etc/apt/sources.list:4 and /etc/apt/sources.list.d/tvheadend.list:1
W: Target Translations (main/i18n/Translation-de) is configured multiple times in /etc/apt/sources.list:4 and /etc/apt/sources.list.d/tvheadend.list:1
W: Target CNF (main/cnf/Commands-arm64) is configured multiple times in /etc/apt/sources.list:4 and /etc/apt/sources.list.d/tvheadend.list:1
W: Target CNF (main/cnf/Commands-all) is configured multiple times in /etc/apt/sources.list:4 and /etc/apt/sources.list.d/tvheadend.list:1
W: Target Packages (main/binary-arm64/Packages) is configured multiple times in /etc/apt/sources.list.d/tvheadend.list:2 and /etc/apt/sources.list.d/tvheadend.list:3
W: Target Packages (main/binary-all/Packages) is configured multiple times in /etc/apt/sources.list.d/tvheadend.list:2 and /etc/apt/sources.list.d/tvheadend.list:3
W: Target Translations (main/i18n/Translation-en_US) is configured multiple times in /etc/apt/sources.list.d/tvheadend.list:2 and /etc/apt/sources.list.d/tvheadend.list:3
W: Target Translations (main/i18n/Translation-en) is configured multiple times in /etc/apt/sources.list.d/tvheadend.list:2 and /etc/apt/sources.list.d/tvheadend.list:3
W: Target Translations (main/i18n/Translation-de) is configured multiple times in /etc/apt/sources.list.d/tvheadend.list:2 and /etc/apt/sources.list.d/tvheadend.list:3
W: Target CNF (main/cnf/Commands-arm64) is configured multiple times in /etc/apt/sources.list.d/tvheadend.list:2 and /etc/apt/sources.list.d/tvheadend.list:3
W: Target CNF (main/cnf/Commands-all) is configured multiple times in /etc/apt/sources.list.d/tvheadend.list:2 and /etc/apt/sources.list.d/tvheadend.list:3
