If folks are interested in the nitty gritty, I wrote a blog post a few months back: https://fusionauth.io/blog/2020/04/15/whats-new-in-oauth-2-1...
And this is a great podcast with one of the authors, Aaron Parecki, talking in detail about the changes: https://identityunlocked.auth0.com/public/49/Identity%2C-Unl...