White Screen

[Flavor]

Now, I'll discuss more about the root problems/symptoms you're experiencing. Some of this information is for other people that come along, because it certainly sounds like you've done a lot of digging/research into this already.

If the screen only stays white, that means that it is not receiving a proper signal from the Pi. There could be many reasons that would happen, but, in this case, I would suspect that the operating system isn't booting at all.

The green LED is the indicator that the correct operating system is booting up. Some people will mistakenly try to boot a "stock" version of Raspbian or RetroPie. Those would also result in a white screen without a green LED even if they were starting the operating system (without being able to see it starting up).

But, in your case, Reidlos88, we have 3 main indications that you have specified.
1) White Screen
2) No LED
3) Using The CORRECT SD Image File

#3 isn't 100% verified, because you didn't mention the actual file name you used to burn with Etcher. As of right now, the latest RetroPie 4.4 file is named Freeplay_CM3_19060603.img.gz and the 4.3 file is Freeplay_CM3_18032101.img.gz. [That will change (probably today), because we have a new updated 4.4 file in the pipeline.] Could you confirm that these are the files you are using?

You are correct in thinking that a Raspberry Pi Compute Module that is not 100% fully attached could cause this problem. Please also confirm that yours is seated like the aforementioned video shows.