not really a dumb phone is it?

My spouse and I set passcodes on each other's Screen Time. Make sure you also check the option to block at end. Problem solved.

you can do most things an iphone does, but you can't doom scroll. you don't have to eject out of apple ecosystem, you get payments, 2fa, navigation, notifications. your iphone can remain as a backup that's always in sync for when you need it (e.g. traveling)