They don't. They discourage it on the consumer end, but that also has good safety reasons behind it. They go a little too far in pushing people to Play Store over other app stores, and require basically any phone with Google Services to have Play Store, but that's a different matter.

They've never tried to dictate rules on what sideloaders, both on the supplier and consumer side, can and can't do like Apple has.

The closest they've ever done to this is use Play Protect against apps like Lucky Patcher. And that's a piracy app that, among other things, patches other applications to do things like bypass Google's payment systems and disable ads.