Oh, and to show that I'm not just some isolated crazy person, here's a list of other instances I've found of this being brought up, sorted by date:
Jan 05, 2016: https://itch.io/t/13163/suggestion-tag-exclusion
Nov 06, 2017: https://itch.io/t/160014/can-i-use-exclusion-filters
Mar 26, 2019: https://itch.io/t/427018/front-page-search-please-allow-multiple-options
Oct 12, 2019: https://itch.io/t/579083/how-is-the-tag-system-here-handled
Jan 14, 2020: https://itch.io/t/653769/can-i-exclude-horror-games-tag
Jan 27, 2020: https://itch.io/t/664720/a-few-suggestions (not the focus, but one of several suggestions)
Jan 29, 2020: https://itch.io/t/666471/filter-by-exclusion
Feb 25, 2020: https://itch.io/t/692147/is-there-a-way-to-exclude-or-ban-some-tags-when-i-brows...
Apr 26, 2020: https://itch.io/t/766168/filter-out-horror-games
Jun 29, 2020: https://itch.io/t/853768/blacklisting-tags-from-search
Jul 11, 2020: https://itch.io/t/867998/excluding-tags-in-searches
Sep 30, 2020: https://itch.io/t/994040/use-exclusion-filters
Jan 03, 2021: https://itch.io/t/1138299/exclusion-tags-feature
...as you can see, people have been consistently asking for this very basic and obvious feature for OVER FIVE YEARS now. I don't want a link to the same four year old broken workaround, I want this problem to be solved. Not just for me, but for everyone. Or if you aren't going to implement this, can you at least tell us WHY.