@KR-01
Depends on how your cable box is hooked up to your Roku TV. (hdmi cable or coax input).
Try going to Settings/System/Power/Power On/ [Last used TV Input] or [Antenna Input]
This will now use the selected option each time the TV is powered on.
Now, before you shut off your TV for the day, make sure to select your cable box and tune to channel 12 before shutting down TV.
Next time you power on the Roku TV you should hopefully be on ch.12 on your cable box.
Roku Community Streaming Expert
Just another Roku user... I am not a Roku employee.
Insignia RokuTV, Ultra 4660, Premiere+ 3921, Express 4k+ 3941, Streambar 9102