@cyoungers
Not sure on other devices...
On the Onn 4K this is what I did to keep it from sleeping and I never see it shut off. The screens just stays on the Home screen when not streaming...of course it still gets the adb reauthorization sometimes...
In Ambient Mode...Make sure that Google Photos, Art Gallery, and Experimental are not selected:
Under Power &Energy...Select Never
Under Developer options... Turn on Stay Awake
I may delete the remembered saved ADB authorizations on one of the devices and relearn it to see what that does.
If that doesn't work may resent to factory and see if that fixes it...