"creating a commit would abandon the branch" is certainly something lost in translation. There are other reasons you may have not liked the UX, largely that if you create branches and then add a bunch of commits after it, the branch head doesn't automatically move by default. There is a config setting you can change if you prefer that, or the `jj tug` alias some people set up.
Auto-commit is still a thing, but you can regain the stuff you like with a workflow change, this is called the "squash workflow" and is very popular: https://steveklabnik.github.io/jujutsu-tutorial/real-world-w...