What keystroke combination put Mac’s display to sleep? When I hold down the Option and Command keys, and then tap the key at the upper right on my Mac’s Apple OEM keyboard, Nothing happens on the Keychron Q6 Keyboard.

Hold Option–Command–Power button* or Option–Command–Media Eject: Put your Mac to sleep.

Control–Shift–Power button* or Control–Shift–Media Eject: Put your displays to sleep.

You can use VIA to remap a key to the power button or media eject and try the key combinations mentioned above. Click on the link to learn more about how to use VIA.