@RustyCrab I know for SailfishOS they have the mir compatibility layer they built. When you buy their cellphone or operating system, that is actually what you are buying, the compatibility layer to be able to run android programs.
Not sure about purism, but they put just as much effort into their operating system and making sure everything works in an ultra free way. Never used it, but never heard anything bad about it.
Pretty much all the other projects are white noise (pinephone, etc.)