Thanks for the informative reply ! I was trying to follow the same fog of war tutorial. Unfortunately, URP doesn't have the "clear flags" option in the camera at all. It stacks cameras and passes the buffer in a very different way. So when the frame changes, the red part just clears to be at the centre of the character (instead of all the area they have traversed).
I have scoured the internet, but till now haven't come across any FOW tutorial for URP. I was using 2D lights, hence using URP. But looks like I will switch back to Builtin Pipeline, as FOW is essential to my game.