Hi there. There is a screen timeout option in settings under display. You may need to set that to a longer time. When you are using Discord are you making video calls when the screen goes black? Is there an option to keep the screen awake when you are looking at it also under settings? Like a smart stay option.
Which Motorola are you using? What version of Android are you on?
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https://forums.androidcentral.com/showthread.php?t=409154