VAR should be really simple and quick to implement
Forget forensic examination of millimetre offside decisions, the tech isn't up to scratch anyway
Forget forensic examinations of accidental handball
Apply the KISS principle
review both in a 5 second window, far more time than the referee had, and if it isn't clear and obvious in that 5 second window then crack on
Follow that with mic'ing up the caravan down south and the officials on the pitch, and playing the reviewed video in realtime on the big screen
Finally, provide a box of bollocks for the VAR officials so that, if it is a clear and obvious error to the 3 in the caravan, they overrule the guy on the pitch
It won't stop every controversial or incorrect decision, but it "should" if used fairly, stop the clear and obvious ones (the reason for the introduction of VAR in the first place)
There, it's fixed, you're welcome