Are there any GNU/Linux distros for mobile that are actually worth using? I'm not aware of any but I'd love to be proven wrong.

As it stands, the only thing keeping my Pinephone from replacing my BlackBerry is better messaging notifications. Calling, messaging (via Matrix), and Firefox are all mostly good enough for me.

Note I'm not saying it's good, but good enough for me. I've been using Arch, as I find the rate of improvement shows in a rolling release distro, and in my experience, Mobian is no more stable.

The closest thing to secure, actually usable Linux distro on phones is Android; if you are serious about security and degoogling GrapheneOS especially. The bad thing is that you have to have a Pixel for that.

Source: I own a Pinephone and has tried both Phosh-based and KDE-based offerings, there is also Sailfish though. Out of these Sailfish is the only one close to usable as of now.

Except in what concerns Google, the Linux kernel is an implementation detail considered no go area for app developers to call into.

Ignoring this advice might lead to application termination.

I think some are getting quite good. I’m following Manjaro/Phosh, and it’s showing promise. I’m not using it for much yet, just watching it develop. I believe other distros are further along.

Yes: Sailfish OS.