Interesting. That code is beyond me. It is 240 KB and I do not know how to start understanding what is going on.
My own thingy is 10 KB and I wrote it a year ago. As mentioned above. Tried doing it with an extension but after finding the thread https://itch.io/t/1018893/a-never-show-me-this-again-please-button I switched to a tampermonkey script.
It will put a cell in a list and apply a css style to all items on that list. It can do more, but that's the core.
So, simple use case with defaults: hover cell, press 1, game gets hidden.
There is two styles to switch between and two lists. And the second style is always used for library pages, even if switched. It can save and import lists and also put developers on the list.
So for your use case with the favorite and the ignore button, one could use list 1 with styles {outline:auto green} / {} as a favorite list and list 2 with styles {display:none} / {outline:auto red} as an ignore list.
As I understand it, you want to make some library viewer as well. You might even save the thumbnails. There is personal database software for managing games, movies, books and such. Maybe one of those has an import feature for Itch games that could be fed with an url list or something like that.