Andrew,
I have now built Limesuite and gr-limesdr from source, and installed gnuradio-companion on 20.04 LTS.
Things are now working as expected, just taken longer than a simple ppa install.
I did have to copy the /usr/local/lib/python3/dist-packages/limesdr folder to the respective /python3.8/dist-packages folder for gnuradio-companion to overcome the ModuleNotFoundError: No module named ‘limesdr’ when running from the desktop launcher. An initial fix was to use this tip at the command line to point at the python3 install location and run from terminal. ModuleNotFoundError:
Kind regards
Mick