Maybe this one? Embedded comments in an iframe, and if you login, there'll be a session cookie, in the iframe. There's no tracking — each blog has its own unique sub domain with unique cookies, and no cookies on the 2nd level domain. Still, disabling 3rd party cookies in Chrome seems to break login:

https://www.kajmagnus.blog/new-embedded-comments

(what happens if you try to post a comment. I think there'll be an error. I'm developing this b.t.w.)