I know its been mentioned many times on here already, but rugby has this nailed. Why not just copy that approach? Refs are micd up, we hear the entire conversation, we see what the VAR is looking at and even if you disagree with the end result as some things will be subjective, the process is 100% transparent.
This whole "clear and obvious" thing, was always going to be a shitshow as it introduces subjectivity into whether something is even reviewed or not.
We just need to be clear when VAR will be used (I suggest goals, penalties/possible penalties not given on field, sendings off/potential sendings off not given on field) VAR checks 100% of these situations. feck all this "it should not re-referee the game" - its literally the whole point of it to make the best possible decision, regardless of who does it.
Edit - the implementation just shows the ego and arrogance of the referee. Yes he makes most of the decisions but it should be a refereeing TEAM that collectively get to the right result. Also, if a possible penalty is reviewed for a tackle on the 18 yard line that the referee didn't give a foul for and VAR sees a clear foul but it was outside the box, then give the free kick, don't just ignore it.