That sounds like a lot of legwork to "Simulate" just one more exclusion.
"Not in Collections," or "Not in Library." I don't particularly often want to do a general search for things I already know about.
It is unlikely that Itch will implement such features any time soon. Until they do, user solutions to these things is what already exists.
You can use the feedback button to give Itch a more direct and specific feature request. The need for some negative tag filtering is known for years. And that it has not been implemented hints that there might be reasons for this. Like, there not being enough people really wanting this feature, not enough people using the feature already there, the feature not being effective on Itch, the feature costing too much to have active and so on.
The ignore your own library is not as much discussed, but in my opinion the more useful feature.
The user interface for the existing single tag exclusion was a one afternoon side project, while I was working on a ignore your own library function. It was so quickly made not because it is sloppy, but because the thing this does it trivial. It just makes the url modification persist and that is a trivial function to use inside a browser extension. I have since then condensed the actual project into a script and released it on the project I made and in comments. /t/1018893/a-never-show-me-this-again-please-button
If you can run extensions, you will want that tampermonkey script. It does exactly what you want. But you do need to set it up and that means clicking on the projects in your library.
That sounds like a lot of legwork to "Simulate" just one more exclusion. The verbage says it's for tags, not categories or genres.
I do not understand what you mean. The script has memory and you set it up once. And you can ignore anything you can filter positive. That means any tags, genres, /directory other filters, and of course: each game individually and also by developer. You press the button once and the game is gone forever. Ignoring things individually is what the script was made for, but you can exploit that mechanism to just ignore anything in bulk that you can filter for, in the browse section. But that exploit has to be set up and that is actually rather quicly done, except it you try to add 100000 items at once. For browsing popular, a few hundred of each tag are enough and you can do that in a few seconds for each tag/genre/other filter.
And I described how you would set up a multiple tag exclusion, because that is what has been discussed in many threads. You filter for each and all things you do not want to see and just put them on your ignore list. This obviously does not catch new releases, but you can add those individually when needed.
There is two ignore lists and you can export and import them. Importing a list means merging with the list you have. So you would make one list for your library and things you have seen, and one list for the things you do not want to see. And if you have special requirements, you can export your regular list, clear the list and import the special list.
The optimal use case is the never show me this again scenario. You see a game, decide you do not want to bother with it in future browsing, and click on it, and it's gone. Forever. Or until you remove it from the list. For that you swith the script "off" and just click on the game again. And by click I mean pressing the configured button. Default is 1.