How can Roon add additional metadata if the album is unidentified? The fallback position is to use the file tags, and if these are lacking, neither Roon nor other music players will know what is playing.
Perhaps you could provide some real examples?
Bearing in mind that anything in your folder view is already in your library, you can manually edit the artist name, title, etc. Simply click on the ellipsis, and select Edit.
You can also list all unidentified albums using Focus, filter on an artist folder, and batch edit.
However, if many unidentified albums are official releases, investing in some time (and money) tagging them is probably the best route. I have my own workflow, which uses MusicBrainz and Discogs. Anything missing I add to MusicBrainz, so Roon will identify the release. Some software, for example, SongKong, will attempt to automatically identify and tag a large number of release in batch.