To add context to Meta blocking Pixelfed mentions, I should remind everyone that Youtube silently hides comments containing "OpenStreetMap". I think @simon and @harry_wood found that out a few years ago.
https://en.osm.town/@mastodonmigration@mastodon.online/113819524597166451
@zverik @harry_wood @simon for what it's worth I once commented on Facebook post by an account actually named <website name>.com mentioning said website.
It got removed as spam ... for mentioning the name of the Facebook page I was commenting on.
And in my experience basically any mention of a URL in a YouTube Comment will cause it to be removed. So I tend to assume they're all basically using a big allowlist these days and blocking the rest.
@InsertUser @zverik @harry_wood at the time I didn't add an url, it was literally just "OpenStreetMap".