Or use the cloud gaming approach and just stream the video, no local engine at all!

I think Denuvo technically does a little bit of this.

I forgot the exact details, but one of the keys that's used to unscramble the bytecode has to be downloaded from their registry server on first launch.

But after that, it's not required.

Although that still never totally protects it. I've seen a fair few number of passionate game communities bring online-only games back from the dead by reverse engineering the server architecture. It's a lot of work, but if you know how the software is supposed to function then you can write the other half of the software that gives the response to make that work.