That's pretty much literally what an OS is! An application that lets you install and run other applications.

I never imagined selling software would be a core function of an OS, but here we are.

You keep responding as if Steam is not a thing on MacOS, it is very much a thing and has been since steam launched.

I am aware it is. My comment is about app stores not being an integral part of an operating system. Or, at least, they didn’t use to be.

OTOH, Linux has had package management for decades.