The feature was implemented by Itch's leafo some 6 six years ago, or so I understood. It never got a gui or was advertised much. Or expanded to work for more than one tag.
The only thing my homebrew extension does, is to use a feature that is accessible by extensions to modify urls persistently. And attach an input box. So you can write in the tag and browse with the excluded tag and do not need to modify the url each time with copy paste.
With a bit of legwork you can simulate filtering multiple tags with the third tool, the tampermonkey script about the ignore list.
Basically you search positive for what you want to exclude. And then scroll down in endless scroll for a bit and then go to top again and press and hold 2, while the css is display: none for list 2. This will add like 50 items per second. Rinse, repeat, for more tags. You can save the lists for later use and import them to combine them differently.
Of course this will not update automatically for new games. But the popular list is ranked by popularity, so you need only add a couple hundred of the top items of the unwanted tags and the top does not change much.
And if you browse obscure tags with less than a hundred games, you might not even want to filter the tags out. The dev and you might be of different opinion about the tag, or you might make an exception for some games, if they are good enough in other aspects.