It's funny: I've never tried to use Rails6 since its release, and now that the latest rails7 has been released, I can say that I've missed the Rails6 version perfectly. On the one hand, my company's projects are still stuck in Rails5, on the other hand, I'm scared of Webpack, not familiar with it, not good with it, and find it expensive to learn, and I'm even more discouraged by the fact that Webpack itself is constantly changing.
More about features and changes made, check out the Rails 7 release note. These aren't very comprehensive but will get updated sometime. If you are running on Rail 6 or lower, then remember that with the final release of Ruby on Rails 7, Rail 6.1 will not receive any bug fixes. You can now update Rail 7 and enjoy the latest updates and features.