Thanks also for the suggestions. Import of settings from the Windows version is one of the things I’m hesitant to do — it would require re-implementing the settings formats from Windows and I’d have to deal with missing action types and other differences in the Mac version.
Regarding backup of settings: Mp3tag for Mac uses the User Defaults system of macOS. If you're familiar with the command line, you can use the defaults tool, e.g.,
defaults export app.mp3tag.Mp3tag ~/Desktop/Mp3tag.plist