IssueTracker

I attach a project to reproduce the issue.

There are 2 buttons: one add a named fragment transaction (which you can remove with back) and the other navigate to another fragment using nav graph.

You should be using childFragmentManager, not requireFragmentManager(). As of Alpha 04 and https://issuetracker.google.com/issues/111345778, back button presses are automatically passed to the child FragmentManager of the active Fragment, allowing you to do whatever FragmentTransactions you want in that child FragmentManager (using Navigation or not).

We can improve the error message though.