An answer from 2017 that has a solution that no longer works. Please consider my options I have given here: Why don't admins relay to whoever made them staff that we need an exclude tag option? - Questions & Support - itch.io
Also, with over 1.02 MILLION GAMES you would think an exclusion option would take priority, especially when it is a highly requested topic. If there are lots, and lots, and lots of discussions about this, then maybe it's an issue that needs to be taken with a higher priority as many of your users and developers are asking this simple addition of your sites developers. Instead of a roundabout answer, you should take the time to send this and all the other requests to someone higher up than waste time telling us a solution that all of us have seen and tried before, as it is the one of the first three search results on google if you search, "Itchio exclude tags" or "how to exclude tags on itchio".
I understand that there is probably a path your team is taking to make additions to the site, but it takes 1-2 people and a few lines of code to alter a search result. and if/then/else statement could be made as an idea, but idk