So. Are you still working on this? Any obstacles to overcome? Maybe I can help, as I tackled quite a few of those. It works frighteningly well so far. Though I have no buttons. Not sure how to make use of the extension popup. I activate the stuff with context menu.
It will be fun to compare different methods of problem solving. The context menu stuff was just the first things I stumbled over - also I lack knowledge in html.
I am stumbling over beginner's pitfalls and idiosyncracies all the time. Like needing to put the script tag in the popup.html at the bottom, instead of the header - or I cannot dynamically change html elements. Or that I cannot reliably use a button in the context menu to load things. Maybe I am using the wrong loading method, but I think it is a bug or idiosyncracy of chrome. The click to indicate a user action is not given when selecting the context menu item, but when opening the context menu... urgh.
Currently adding bells and whistles. The core functionality works - I can style items and they stay styled untill unstyled.
I even had zipping of the data at one time. Which was fun in a sick way. Blobbing, streaming, zipping, converting to base64 and writing to storage. It worked. But it was too slow for page opening and changes. But that's what you get, if you stresstest with literally millions of items to ignore. Yes, it worked. But I changed from that to operate on the storage directly and just ask unlimited storage permission. There is a 10MB barrier. And if you do not use Set or Map or Arrays, but Objects, it is rather straightforward to store and update.
As a bonus, while working on this, I thought to myself, it should actually be trivial to make a button for that exclude feature, so many people are asking about. And it was. I figured, if the extension would work, people would use it to ignore games with tags. That is why I tested with very big lists. Better to also give that exclusion functionality as well, so there is less lists to do.
I made a separate extension out of it. https://redonihunter.itch.io/itch-browse-tag-exclude