kebab_definite
@CrYpT999 gave you part of the answer. You'll want to adjust any of those settings on Lock Screen as the ambient display has to do with anything happening on the lock screen. Any idle audio/video playback could also impact that.
Also if you swipe down from the top of the screen twice, where you can access your control toggles ...at the bottom you'll see some options to push (settings, profiles etc) there will also be one with a number. That will list apps running on your device. You can try to end any them there, maybe something is just constantly running in the background that you can catch.