Another weird issue I just learned:

Currently, I have my 'Zelda Classic' folder on the desktop. It works as well as I'm getting used to (a bit choppy, but otherwise playable).

On my old computer, I had this folder inside another folder. When I put the 'Zelda Classic' folder into that other folder, the z-launch doesn't work.

Not sure if that's related to Windows 10 or not, but it's weird.