Take a deep breath. Really. This be a VERY long, detailed, step-by-step guide on how to tweak unrooted Android smartphones for maximum privacy and security, covering basic considerations, pragmatic approach, device purchase and long-term patching policy, installation and first-time setup, sensors - Wi-Fi, Bluetooth, NFC, and Location, biometrics, every configuration inside Settings, applications - system, permissions, special access, required and recommended list, how to install, and use, Firefox browser and adblocking, accounts and accounts linking, analytics and diagnostics, personalization, Google services, messaging apps, automatic image and video download, anti-malware software, VPN software, data backups, cloud, encryption, and more. It took me some 30 minutes to read my own stuff. Just sayin'. But this should be highly useful, and perhaps even entertaining. Have fun! https://www.dedoimedo.com/computers/android-security-privacy-guide.html Cheers, Mrk
the solution is very easy: dont use a smart phone, in any way - this means also not an older one with phoning and sms only.
If you want an Android phone with maximum security and privacy, also take a look at GrapheneOS.(Previously CopperheadOS.) Tons of hardening, attack surface reduction and many interesting security features: https://grapheneos.org/features Though so far it is only available for Pixels due to strict hardware requirements.