By default it is blocked although it's usually one of the first things I turn off. I always have at least one or two apps that aren't on the play store.
I hope that Google doesn't block this feature and turn entirely into a walled garden.
As soon as they do, they die with users like me. I am pretty tolerant of the eco-system lock in because I can so easily opt-over the wall when I want to. If they change that, I'll go to the next platform that respects my ability to make choices for myself, even if they don't match what some people in power in California thinks I should choose.
I hope that Google doesn't block this feature and turn entirely into a walled garden.