I manually tagged an untitled album in Roon as Jazz, and it does not appear with other jazz albums, but in a category all it’s own.
Correct, the thing you added is a tag, not a genre. Tags are for user-driven organization (similar to how tags work in, say, Adobe Lightroom). Genres are an organization of content into a hierarchy provided by one of our metadata sources. They do not mix.
Then how can I manually identify an unidentified album as belonging to a particular genre?
We are working on more editing/grooming functionality in Roon, but for the time being, this is not supported.
Ok. I guess I’m surprised there isn’t any way to use the metadata already in a file.