Hello,
I did similar things, and I have experience with DVB TV tuners, codecs and drivers on different Linux based OSs, including Ubuntu.
I also did different setups using MythTV, VLC and Kaffeine under Slackware, but Tvheadend is more straightforward, and requires less tinkering :-)
Maybe I can make it work without reinstalling, just by reconfiguring what you already have.
On my Ubuntu 22.04 and Tvheadend git-4.3.0 version HW accleleration works with an i5 6th Gen, so worst case scenario this versions can be installed and configured, but maybe it will also work with your current configuration.
All the best!