Itch has freestyle tagging. If you think something is a tag, or is used as such, just enter it in the tag box. I believe I complained a few times, that it says "Select a tag". That's misleading. It gives the impression that this shows all the tags there are. Also the page of tags is linked to by a link called View all tags. That's very misleading.
You can just write any tag in the box. And when publishing a game, you can also chose tags freely. Of course, if you chose tags that no one else uses, the tags are useless.
https://itch.io/games/tag-launch
https://itch.io/games/tag-toss