How to Enable Developer Mode Disabled by System Policy on Chromebook
Developer mode is often disabled for a reason
{only try this if you own the actual device)
again you must OWN the device as doing this on a school or business owned device could end up with trouble at your door
(i just done this on a refurbished Chromebook that was sold 2nd hand)
once you follow this step you will not be able to revert back to the current position, if you still want to continue
also make sure the device has not been stolen and sold on to you cause again TROUBLE will come a knocking