Would be great if we could delete a tag that is not used.
It should be displaying only the tags that the currently selected collection/folder has. It may be a bug actually. Can you show an uncropped screenshot of this?
Here is the screenshot uncropped. This tag was here by default, I didn’t created myself because for me this tag should be a collection instead of tag.
We already have fixed this issue and soon it will arrive with the next FontBase update.