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.