Roon shows button "Other Versions" - but there is no other version

How come?

This is shown any time the album matches an edition on TIDAL.

Ah okay thanks @mike.

The trouble is, if you already have the Tidal album in your library, it still comes up with ‘other versions’ which links to the same version on tidal - see example below

This is by design. The version in your library could have edits or favorites, could be incomplete (like if you only added a single track to your library) and will also reflect library-specific links, like if you have other performances of a particular song, or if a given composer features prominently in your library.

This link takes you to the “untouched” version of the album on TIDAL, as distinct from the one in your library. It’s a bit of a weird concept when none of the distinctions I mentioned above apply, but for consistency we need to give you that link.