BluePhoenixWrites As of an update from either last year or earlier this year (I can't remember which), all tags for novels have to be chosen from that "All Tags" list. There really are as few as there appear, and you can't input your own or edit the existing tags. Also, tags can't be edited from the story page/profile and have to be edited through Inkstone (or the "Write" tab on mobile), though that was true before the tags update.
(...That update still irritates me for wrecking my novel's tags and making one a fanfic tag, but that's aside from the question.)