Unlike SketchFab, Fab only allows the use of tags from a supplied list when submitting models.
This would be OK if there was an extensive list to choose from - but there isn’t.
For instance, I sell a number or buildings built in the ‘art-deco’ style but have no way of tagging that despite it being something that may be of importance to a buyer.
Adding new tags was a much better system in SketchFab and resulted in better search results when being specific is important.