I am using Android 11 and Samsung's OneUI 3.1 (updated as of May 1, 2021), and it'd show the "Lock" icon right at the center of the screen and dim everything down after 3 minutes.
All the other OnePlus or Xiaomi phone do not do that. If I follow the instruction online to go to Settings -> Lock Screen -> Lock Type to "None", it is still happening. Is there a way to disable it totally?
P.S. There was a "Screen Timeout" in one of the settings option, but (1) It is set to 30 minutes but the phone still shows the lock icon after 3 minutes, and (2) I'd like to set it to "never" but there is no such option