@koyax and this demo video is actually quite old :)
In the mean time I've also managed to enable the back-gesture in Android and hide the back button (thanks to @larma for the help there), audio routing to earpiece works, proximity sensor works and much more. The only thing that's really hard/impossible so far is making android aware of the cellular network.
I actually wrote an incomplete list of known issues, just added that to the repo: https://github.com/jonas2515/alien-everywhere/blob/main/other-docs/known-issues.txt