None of these examples are of actual separate registration/ownership of a 3LD from the parent 2LD. Cloudflare owns the domain for myproject.pages.dev and hosts all the relevant infra. Not to say that there isn't a different entity represented by the 3LD than the 2LD but it's not exactly the same.

Also I would not consider the examples of tumblr and reddit to be relevant. A person's blog on myprofile.tumblr.org is still the tumblr organization. This would be true for reddit even if they didn't redirect. Reddit admins moderate content on all subreddits.