Why don't you try unstable packages from Doozer - https://apt.tvheadend.org/
I have yesterday upgraded my RaspberryPi 2B running "Buster" from stable to unstable:
tvheadend/raspbian-stretch 4.3-1983~gb8710206e~raspbianstretch armhf [upgradable from: 4.2.8-34~g24a2f59e9+rpt1~buster]
tvheadend/oldstable,now 4.2.8-34~g24a2f59e9+rpt1~buster armhf [installed,upgradable to: 4.3-1983~gb8710206e~raspbianstretch]
Same for my other setup 3 x USB DVB-T2 + 1 x USB DVB-S2X tuners and all seems good and working .....
Here is what is available:
#Unstable Debian 09 Stretch - amd64 and i386
#deb https://apt.tvheadend.org/unstable stretch main
#Unstable Debian 10 Buster - amd64 and i386
#deb https://apt.tvheadend.org/unstable stretch main
#Unstable Debian 11 Bullseye - amd64 and i386
#deb https://apt.tvheadend.org/unstable bullseye main
#Unstable Debian 08 Jessie - armhf - RaspberryPi
#deb https://apt.tvheadend.org/unstable raspbian-jessie main
#Unstable Debian 09 Stretch - armhf - RaspberryPi
#deb https://apt.tvheadend.org/unstable raspbian-stretch main