You asked for tools/methods.

> I've spent hours and hours unsubscribing, deleting, uninstalling, toggling settings,but then I find myself reinstalling, resubscribing

You already know the tools and methods. This is more of a psychology issue rather than technology. You need some sort of dopamine detox. I'm not a professional, there are probably professionals out there that can help but here's some random thoughts of what that might look like:

* Take a week off work and turn off all notifications. Tell work you are unavailable.

* Write anything important down on paper that happens in the next two weeks: birthdays, events, appointments, etc. so you don't miss them. A paper calendar planner works.

* Turn off the phone if you can. If you need it for travel - uninstall everything unnecessary and keep all the notifications off. Phone, maps, airline, Uber, SMS, web browser are really all you need. You could ditch the airline app and just get paper boarding passes.

* Do something, anything, that doesn't involve computers/phone and notifications.