The best option is to create an issue ticket on github so the developers can investigate and fix the crash. You should capture a debug log of the crash and attach to the ticket. A guide can be found here.
I tried but can’t reproduce your issue. Double tapping the “To” email address on the reply doesn’t drop me back to the inbox. It displays a box allowing me to copy or remove the email address.
You are right: After double-tapping the address, a selection is offered to either copy or delete the address. But when I then (while this list is shown as an overlay) tap on the original address again (not the one in the selection list), the described scenario happens.
Before I might have been unprecise as I might have tapped three times instead of two onto the mail address.
Unfortunately I’m unable to reproduce, no matter how many times I tap on the “to” address. I’ve tried with names from Android’s contact list enabled and disabled. Maybe another user on Android 16 will have better luck reproducing your crash. I’m running Android 15.
A debug log will reveal more information about the issue.