Android. Calyx or Graohene OS. Don't install google services / GApps / GSF. Minimise the number of installed apps. Disable apps automatically if unused for a period of time.

I've been using calyx os for about a year now, i really like it and I'll only be using a custom rom from now on. but I'm thinking about giving graphene os a go. I would like to know if there is much of a UX difference?

always-on VPN, always off: bluetooth, location, microphone (unless strictly necessary); use Tor browser often; minimize/uninstall default corporate apps

Buy a 6th or 7th Gen (or latest on release) Google Pixel for the longevity of the support window. Go to grapheneos.org and use the web installer at graoheneos.org/install/web to install GrapheneOS. Profit 🔒📲🚀