This was all about the news probably 2 years ago. Chrome uses a new api manifest that does not allow for changes in websites like blocking specific type of content. Once manifest v3 is fully implemented and enforced there will be no way for ublock origin to work correctly anymore.
The word “just” is doing a lot of heavy lifting in your edit. The replacement for that dependency doesn’t allow an extension to work as an ad blocker as effectively as the thing they are deprecating. This is deliberate.
Could a grease monkey script do something similar? I’m probably just talking out of my butt, but it seems like GM can sometimes do things easier or better (or just at all) that extensions can’t or won’t do.
The one and only thing keeping me on Chrome... well, Ungoogled Chromium... is the webassembly performance which is just abysmal in comparison on Firefox, sadly.