I wish it was feasible to have alternative mobile systems, but it's not really. You can't simply give up every popular app for a system nobody else uses or develops for. Sailfish has Android emulation, but good luck running banking apps without Google SafetyNet. Even pure Android ROMs, like LineageOS, can't do that. Also good luck with proprietary firmware for mobile networking and cameras. Another thing that usually…
Perhaps the solution for such a phone is to make PWAs feasible for every kind of app?
I guess it would need a few essential built-in apps (something like an Apple Health analog) but hopefully the rest could be web apps with extra privileges, if needed and approved by the user.
Is geofencing already possible with PWAs? I.e. location based events? If not, that would also have to be a builtin (helper) app.