I would like to know if there is any easy way to find compilations that are not tagged as such. Maybe someway to search for same album with different artist? How could I do this?

The first question would be "How do you compilations as such?"

On its own, mp3tg does not compare two (or more) files with each other.
You would have to export the file data and then compare the exported data with a different application.

The other possibility would be to filter for album names that are likely to be compilations, e.g.

%compilation% MISSING and %album% HAS "Ambient lounge"

On the other hand: there are loads of "Greatest Hits" albums, all by one particular artist each - so they would match the criterion "same album with different artist" ...