Yes, the `guid` field in RSS and the `id` field in Atom.
Of course a lot of feeds also get this wrong and change the GUIDs for existing entries once in a while which results in strictly compliant readers showing you the entire feed history as new. Really annoying.
The latter is annoying, I agree.
¹ It is an NNTP interface so the article is superseded; https://feedbase.org/about/ - if you don't want to see updates, you can configure your newsreader to skip supersedes.