Found out how to get it working, but it doesn't block the tag I want blocked
Viewing post in Actual working tag exclusion
That's strange.
If this is the genrefilter, the games must have the genre set as their main genre. It will not block games that have that genre set as a regular tag.
If this is the button for the single tag exclusion, you need to be logged into your Itch account while browsing for the feature to work (has nothing to do with my script). And you need to enter the tag as seen in the url without the prefix. So if the tag is shown as genre-visual-novel in the url, you enter visual-novel. If it is tag-3d-platformer, you enter 3d-platformer.
Both those tag blocking options work on my system, as I just tested. I am on Chrome.
You need to enter gay in the box.
To use the exclude feature, you transform a tagname into the url modifier as shown here
https://itch.io/games/genre-visual-novel
https://itch.io/games?exclude=tg.visual-novel
What the tool does is, to give you a box to write in "visual-novel", so you do not need to manually add "?exclude=tg.visual-novel".
And it also makes this url change persist. For a recurring search, you can also just simply use a bookmark, no need for a tool.