Android 9 works flawlessly on many SD 801 devices. I believe it's the last version of Android to see such active development on this 32-bit SoC.
I've just installed it on my old HTC (which was also stuck at Android 5 and apps last updated ~2 years ago, even the autocorrect stopped working), and it's surprisingly usable.
Increasing the minimum CPU frequency and boost time makes it feel much snappier, and everything works as it should, even Google Assistant with hotword activation. Some overclocking should provide even better performance, but it would likely need a new battery.