They could do what Windows has done, and build OS code that checks if the running application is a known-legacy game, and lie to the game about various capabilities so that the game runs well and looks good.
Not sure how much of that is still around but it was rampant for many years and likely a key to Windows success in gaming.
> They could do what Windows has done, and build OS code that checks if the running application is a known-legacy game, and lie to the game about various capabilities so that the game runs well and looks good.
Or, even simpler (and AFAIK modern Windows does that too): if the running application doesn't say in its application manifest "I'm a modern application which understands the new things from operating system versions A, B, C and features X, Y, Z", you know it's a legacy application and you can activate the relevant compatibility shims.
Not sure how much of that is still around but it was rampant for many years and likely a key to Windows success in gaming.