Even after reinstalling (using apt), version 1.2 of Tuxguitar in Ubuntu 20.04 plays sounds, but the GUI won't show animations of the notes being played in the current track; the play cursor just stays motionless while the MIDI audio plays until a page refresh is performed, either because the audio arrived to a note in a position on which the page needs to be automatically scrolled for the note to be shown, or because I mouse-scroll.
I had exactly the same problem as described above. I visited the website of the project Official site of Tuxguitar and downloaded the package for Ubuntu (x86_64 architecture). Then I run
dpkg -i <package-name>
and although the console showed some errors, the program started normally, solved the problem and even the sound was better. At the moment of writing this answer, I have not verified if every function works well, but at least for playing, it seems to do it. Hope it helps you!PD: After this installation is necessary to run
in order to avoid leaving broken packages. This happens because the version installed following this process is not within official Ubuntu 20.04 repositories.