Screen light sensor

Why are you covering the sensor? It isn't the light sensor that you are covering, it sounds like it is the proximity sensor. However, I've not seen any app playing a movie/video blank the screen in that way. I just started up a video on my iPhone X with the TV app that is part of the Apple iOS, and no matter what part of the screen I cover, the video continues to play. You do not have the option to turn off the proximity sensor.

Please explain exactly what you are doing and what happens. And the colorful language is not necessary.

What version of the iPhone are you using, and what iOS do you have? I've just opened calculator and wiped my hand all the way across the screen and no change. The proximity sensor will only blank the screen if you are using the telephone and have it up to your ear, or you put your hand over the proximity sensor.

What troubleshooting have you tried? User troubleshooting steps include restart, which is powering the phone off and back on again, a force restart, restore from backup, restore to factory; testing after each step. If you get all the way to restore to factory and set the device up as new, not using your backup and test it and the behavior continues, make a Genius Bar appointment at the nearest Apple Store to have the hardware examined by Apple.

Force Restart:

A force restart won't erase the content on your device. You can force restart your device even if the screen is black or the buttons aren't responding. Follow these steps:

• On an iPhone X, iPhone 8, or iPhone 8 Plus: Press and quickly release the Volume Up button. Press and quickly release the Volume Down button. Then, press and hold the Side button until you see the Apple logo.
• On an iPhone 7 or iPhone 7 Plus: Press and hold both the Side and Volume Down buttons for at least 10 seconds, until you see the Apple logo.
• On an iPhone 6s and earlier, iPad, or iPod touch: Press and hold both the Home and the Top (or Side) buttons for at least 10 seconds, until you see the Apple logo.