So as i said in the title it goes black after a period of time, you can replicate it if u leave minecraft launcher in the background for atleast 1 day without interaction, also what could help is keeping your mac on and just using lock screen (pressing power button on macs with touch id) to keep your mac on. I dont have a screenshot right now but will provide when it happens.

a fix is to reopen your launcher.

i uploaded what happens after the time