I'm using Rocknix on an android handheld and it feels so powerful to be running 6.18 mainline kernel with all the modern features I want despite having to build stuff from source since the package manager only has a small list of stuff mostly meant for networking (Entware).
Even though its in beta for my device (AYn Thor), it works so well after only 4 months of development that I'm genuinely reaching the point of perma install and removing the stock Android install from the device.
I would pay cold hard cash for an OEM to do the same with PostmarketOS. Throw in proper open source kernel modules and use Steam's upcoming waydroid fork for Android compatibility, and then throw that sucker in the market and watch Google try to litigate it out of existence.