I guess a year late Google might release sone ad CDN on their domain that embedds third party ads and then you are out of luck. Same as Microsoft already did that with news. They try to embed themselves as gatekeepers here too.
Manifest v3 extensions have access to DOM via the content script (same as Manifest v2). Why would they not do cosmetic filtering? Is that something uBlock Origin developers announced?
Presumably because, as the addon name suggests, it is a 'lite' blocker. Declarative network blocking is much more efficient than script injections, so that is used exclusively.
If you want cosmetic filtering, the original uBO is always available.