I just randomly found a OnePlus with a community build of PostmarketOS (Alpine).

I would not use something based off Ubuntu, but the general Linux Desktop is either insecure (traditional apps) or too resource intensive for phones (flatpak).

Also the boot process is way less secure than on a Pixel with the separated Secure Element and all the verification mechanisms.

In general Android uses hardware encryption, profiles are seperately encrypted, and it uses an equivalent to the TPM for that. Many Linux distros are just catching up on that.

Updates can be equally stable and in the background when using rpm-ostree.

Idle battery life is worse. My old GrapheneOS phone that I use as an mp3 player lasts for 2 weeks.

Tons of Apps rely on Android libraries and Waydroid is very outdated currently. If they update to Android 14 and if you use a base OS with SELinux, the Android security model is intact. (The Android sandbox relies entirely on SELinux, without SELinux Apps can break your phone or invade it).

On Android you have the work profile, which allows you to run a set of isolated apps next to the others, apart from the normal App sandbox.

Android is pretty great and GrapheneOS is the best variant of it, if your priorities are

1. Stability (reliability, not some weird Debian stuff)
2. Fast updates, often faster than Googles or slightly behind (as they are no Google certified OS they dont get early access, UNLIKE Fairphone which still manages to not ship updates for months)
3. Security, Privacy by core design