I've just tried this out on a Raspbian 64-bit install.
1. Make sure your install is up-to-date. Do
sudo apt update
then
sudo apt upgrade
then reboot.
2. Ensure you have enough space on your SD card - at least 1Gb.
3.
git clone https://github.com/tvheadend/tvheadend
4.
cd tvheadend
5.
AUTOBUILD_CONFIGURE_EXTRA="--disable-ffmpeg_static" ./Autobuild.sh -t raspbianbuster-armhf
6. The build script will complain about missing packages. Install them manually then repeat. After the build completes your new package will be found in the directory above the current one and will be named
tvheadend_4.3-{github commit no}~raspbianbuster_arm64.deb@.
7. @sudo apt install -f ../tvheadend_4.3-{github commit no}~raspbianbuster_arm64.deb
8. The installer will ask to install 142 extra packages(!). It will then ask you to choose a username and password for your tvheadend administrator.
9. When the installer finishes tvheadend should be running. Point a browser to
{your pi IP address}:9981
and log on with the user and password you just chose.