There is no simple path.

There have been multiple attempts to legislate a subset of what the parent poster is asking, and they have been met with a torrent of lobbying by the entrenched tech giants. Most recently California's BASED Act, the App Store Freedom Act last year, the American Innovation and Choice Online Act some years ago. If your state and federal legislators can't enact change what hope does anyone else have?

Even the places that have successfully legislated this are struggling with enforcement - EU is dealing with extreme and prolonged compliance issues three years into enactment, Japan's FTC is having to form a new bureau just to police Google and Apple's malicious compliance.

> There is no simple path.

As with most broad societal things, I don't think anyone thinks so either.

There is for sure a "simplest way" of doing it though, question is what that is.

> Even the places that have successfully legislated this are struggling with enforcement - EU is dealing with extreme and prolonged compliance issues three years into enactment

Huh? The EU does not mandate countries to implement laws around "OS must allow the installation of an alternative OS from any third party", I'd be very aware of such a law if it existed I feel like. Are you talking about some future regulation they're discussing or something?