How to stop youtube from playing constantly

Go to Settings --> Screen Time --> App Limits

And then set a time limit for youtube.

When your time limit is up, a screen time block will show up and you will be unable to play anything anymore.

When this block is open, the phone/tablet/other device is able to sleep.

For example, if you want to listen to relaxing music and you don't want the device draining all your battery for the entire 10 hour video, you can set app limits for an hour, or 2 hours, or whatever time. If you've been scrolling on youtube for 3 hours today, you can set the app limit to be 4 hours.

When you are done, just go back to app limits and turn it off.