A new feature or channel should be added with Sleep Timer functionality. It should be like the "TV Off" channel that was added in a 2020 update that works with the TV CEC function to allow the Roku to send a "power off" signal to the TV at a specified time or specified number of minutes/hours.
Note: Please, don't suggest using a inline power timer. This is dumb, as I go to bed at different times and have no desire to dig behind the dresser every night, nor do I want to go and setup a timer on some Smart power strip. Also, I'd rather leave the TV with power, instead of basically pulling the plug out of the wall.