Sailfish tried and failed. Various Linux distro also tried and failed even harder. Consumers at large just aren't interested in anything other than iOS and Android.
The problem is - linux (outside on server land and maybe SteamOS) is everything but (regular) user friendly.
When people buy a new phone the expect a smooth experience without any major inconveniences and uniform UI. And apps. Lots of apps. Full of features and mature UI. Linux mostly have none of it.
The Linux experience on a decently powerful mobile device (i.e. not those open-source phones that perform like a 2010 smartphone) is perfectly fine. I find the Plasma experience to be a little lacking, but the Ubuntu experience is good when you find a phone UBPorts works on. Phosh (GNOME) works better on mobile than it does on desktop for a lot of things (multitouch touchpads come close to mobile in terms of smoothness).
Consumers didn't pick up Windows Phone or HarmonyOS enough to matter either. Access to the two common app stores is crucial for user adoption even when the UI is good.
Users need a new feature or a new power to justify transition. Learning of new OS is not free. Someone should reuse Android UI, but upgrade the OS to full Linux.
Mimicking the Android UI and UX is very trivial. The hard part is getting the OS to run on the mobile device in the first place. On top a tonne of custom drivers, it also requires way to either get accepted by the OEM locks or a way to bypass it entirely. This is getting harder by the day even with Android custom ROMs.
