Althought I still leave it marked as "beta", it should be already quite stable. Look at: Release notes / new users may want to look at "getting started" / AppImage should run on all recent linux distributions - see FAQ.
For Ubuntu users its recommended to install native package from NixNote PPA (although the AppImage version will also work).
More recent AppImage build may be available on Dropbox.
robert7/nixnote2
v2.1.0-beta3
on GitHub
pre-release5 years ago