Yes, the software (at least the not Play-store parts, into which more and more functionality is moving) is nominally open-source. The restriction is on hardwar

Yes, the software (at least the not Play-store parts, into which more and more functionality is moving) is nominally open-source. The restriction is on hardware - phone manufacturers that wish to sell phones with Google's software preinstalled are contractually forbidden (by Google) from selling versions with Android forks. Meaning you cannot hire any phone manufacturer if you want to sell phones with forked Android installed - you have to set up your own production lines. You could root phones, but then the many apps (such as banking) that detect this will refuse to work. You would not have a commercially viable product, because only geeks will buy it. Essentially, Google made sure that any kind of privacy-first alternative cannot develop, because it would involve burning too much money, even for billionaires.