I co-run two tech companies and am reachable during office hours which are mostly spent at my desk, and when I am not working I am not reachable by work, and I trust my team.

If you modify your preferred lifestyle in any way for work during personal time, you are still working.

If a company wants you to be reachable 24/7 then they need to give you a pager and a salary based on a 168 hour work week, not a 40 hour work week.

Just because everyone else lets themselves be exploited does not mean you need to. Make the ~40 hours count and work circles around everyone else, then disconnect.

Android profiles with just the the pager stuff installed/enabled would probably work?

And a long/annoying password for the "main" profile, with banking and all the other stuff maybe

I use the app screenzen. It rations distracting apps and retrains you to use your phone as a functional device again. I now only use my phone for messaging, emails, maps and spotify, but can still access Chrome when I need. A perfect balance.

Pagers take SMS. The problem is finding modern pager service.

PagerDuty can send you an SMS or call you, so wouldn't that work with a dumb-phone?