Thank you for the information on Backtap and Reachability! I know about Reachability as I accidentally activate it from time to time, and I've read about Backtap somewhere or other – but I confess I thought it was more like a 'go back to last used function' feature, rather than actually tapping the back of the phone. Good to know, for if/when there is no home button option. But I'm sticking with the good ol' button + swipe up for control centre for now. If I'm quickly turning the torch or camera on I'm almost always using the phone one handed, plus my thumb is dodgy so I don't want to tax it any more...
It's hard to say about the glass – I always have my SE2020 in a case, and it's black not white/starlight – but I do think there was a subtle difference, in a good way. I will evaluate more closely once I pick up the new phone.
You know it's funny...I've typed a lot in this thread about the differences between Touch ID and Face ID and how I like Touch ID better...and that's still true. BUT in going over backtap I came to realize that the muscle memory IS starting to establish itself, and I'm clearly doing things automatically. Even though I was "practicing" with backtap this morning as I composed the response, I caught myself automatically going to swipe up from bottom instead of using it. It's a relief, actually. I look forward to seeing whatever Apple's next attempt is as far as these basic interactions go.