(Solved) Screen blanks when watching video on browser

With power plugged in I have set power saving setting with everything untoggled.
If I do not hit a key screen turns blanks and HDMI shuts down. Very annoying.
Obviously I have a powersaving setting somewhere that is causing this.
Problem is what is causing it.

Two places to look:
system settings → workspace behavior → screen locking
system settings → power management (it sounds like you’ve already been here)

Solved Thank you. After changing both settings and rebooting situation resolved itself