I mean, Android is mostly Linux. I don't think the kernel is the issue. The issue with librem is that they put very little effort into the basic user experience of the software.
Maemo was gtk+ based and many Gnome applications ran really nicely. Eg Gnumeric was great. The desktop dev environment worked so you could port or write stuff from scratch then load it onto your phone. apt-get worked - apt was the app store iirc.
But who cares that stuff?
It was as slick and nice a user interface as the then recently released iphone! No really, I'm not making that up. Fold-out keyboard was terrific too. Way, way ahead of android at that time and arguably still. From memory the touchscreen on the iphone was better but nothing else was.
Microsoft bought nokia and killed it. Nothing has been as good since.
Only the Java/Kotlin userspace and the small set of NDK libraries are considered official and stable.
Anyone that ventures outside this path and isn't an OEM doing their own Android distribution, is on their own if the application actually works at all when deployed via the PlayStore, as the Termux guys eventually found out.