In addition to "essential" apps, like the early versions of Pokémon Go(?) that bizarrely needed to be sideloaded IIRC, and running your own (unpublished) apps - there are the numerous vendor-provided apps and app stores that avoid the play store gatekeeping. (of course, the vendors should be gatekeepers here..)

Then there's f-Droid, the people that run without Google apps (alternate roms).

And then there's "Android TV" that has a "different" play store due to the TV profile being different - but allows sideloading of apps like zerotier(VPN) or chrome - that work fine on TVs - but unfortunately isn't flagged as supporting TV in the Manifest.