I'm using iOS Content & Privacy Restrictions to dumb down my Iphone SE as much as possible while retaining the needed functionality (Calculator, Camera, Notes, Calendar, Clock, Phone and SMS). I uninstall other apps that can be removed. Safari can be disabled using Content restrictions. I install Here Maps, download offline maps for the nearby regions for when I need navigation. Data & WIFI are always off. The phone is not signed in the app store. Content & Privacy Restrictions are protected by a pin code that I write down and store in a relatively hard to reach place. This way I have a relatively modern phone that is not a distracting toy.

I could get a dumb phone (I used one up to somewhere in 2018), but currently there is no dumb phone that would take some half decent photos and provide a possibility to navigate offline.