There is a feature on the Samsung Galaxy S20 called "Smart Stay" that lights up the screen as long as you look at it with your eyes.
This is detected by the front camera, which uses an image recognition scheme to determine whether eyes are looking at the display or not. If this is the case, the display remains active and illuminated as long as you look at it, otherwise the screen time-out is activated. LINK
The Smart-Stay function is useful if you want to set the screen timeout to 15 seconds. In this case you almost have to activate Smart-Stay to be able to use the smartphone. If Smart-Stay is not yet activated on your Samsung Galaxy S20, this function can be activated in the Android settings as follows
Enable Smart Stay on Samsung Galaxy S20 Smartphones
1. Open the settings of the Android system
2. Select "Advanced functions
3. Go to "Movements and Gestures"
4. Select Smart Stay
Activate the controller to turn Smart Stay on
This means that the display of the Samsung Galaxy S20 will now remain illuminated for as long as you look at it.