Though, as the narcs are quick to point out, Android 'is' Linux.

So really, the alternative is proper GNU/Linux (or as I've recently taken to calling it...)

Related recent discussion: https://news.ycombinator.com/item?id=50051530

Yes, let's throw away a fully mature smartphone OS (AOSP) and replace it by something that does not even have proper app sandboxing. /s

The alternative are other AOSP-based OSes like GrapheneOS and Lineage. Once they are used widely enough and funded enough, they could fork AOSP when needed. In some sense they have already soft-forked in that they use major and QPR2 releases, but put a lot of patches on top to fix issues, improve security, etc.

GrapheneOS has an estimated 500,000 active installs now, apparently LineageOS has 1.4M active installs. Probably around two orders of magnitude more than traditional Linux desktop-based phones, which have been trying since, checking notes, Maemo in 2005?