At this point? Reliable emulation that can run 99% of Android apps, to provide a bridge until the platform is interesting enough for people to develop for it "natively".
I think the easiest way to do that would be to run Android in a VM.
If you expect to be "essentially android, but a little different", containers make sense. If you want to build an entirely different mobile OS, but provide Android compatibility, I think a VM is much more likely to give you the flexibility to not defer to Android design decisions.
Actually, if you rely on the app, you really on the Android SDK which is not open source.
Now if you could run AOSP but your own apps built with an open source SDK, that would be a different story. Some people seem to really want to do that with PWAs. I personnally tend to hate webapps, but I have to admit that they can be open source.
If your answer is "don't use them", then you're not living in a country where the vast majority of communications are done on WhatsApp or Signal, good for you I guess.
Sony's cameras used to have an Android userland that they used for their PlayMemories apps. No idea how exactly that one was implemented though, but it should be possible to get Android apps without going into being an Android fork.