My Roku ultra will turn itself and TV back on after I turn TV off and the device goes into screen saver mode..
Roku Ultra never turns off, so, it isn't turning itself on. It may be turning the TV on, though.
If it is the screensaver that is turning the TV on, why don't you just disable the screensaver? Settings > Theme > Screensaver wait time > Disable screensaver
DBDukes
Roku Community Streaming Expert
Note: I am not a Roku employee.
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I have noticed the same issue after maybe the July 2021 update.
I turn the TV off, try to go to sleep, then a few minutes later the TV turns on!
I have an older LG TV that turns on after I turn off my Apple TV. It does not do it with a Roku device or a Chromecast with Google TV, or a Firestick. I can eliminate this by turning of consumer electronic control but then I lose the ability to turn TV on with Apple TV so I have chosen to live with it. You might try your consumer electronic control settings to see if this eliminates the problem.
It doesn't do it every time, maybe once a month.