Add --options=runtime to your codesign invocation.

Feral Interactive Hitman 2016 port had the same issue, because the application name contained the ™ character. But on macOS 11.3 beta 2 I can run it, so probably it has been fully or partially fixed (tested only on AMD gpu).

Enable the "Main Thread Checker" and see if you are calling some AppKit methods from the wrong thread.

The preferred GPU can be selected in the Simulator File -> GPU Selection menu.

Is your costumer's 4k monitor set to a Hi-DPI mode or not? Try to use the NSWindow backingScaleFactor property, mainScreen could return a different screen. Could be a 10.14.1 bug, any reason to be on that buggy version?