Opus with *.ogg extension not editable

[Florian]

I'm aware of the situation and commented on this issue before

Tag does not show up for .opus files renamed to .ogg

You're correct and this is exactly why it's not the same as renaming mp3 to flac. Mp3tag doesn't support codec detection inside Ogg containers currently and assumes Vorbis by default. It's on my list, but for the time being, Opus needs to come with the *.opus file extension to be usable inside Mp3tag.