Haven't seen it, so don't know how close it was, but was it offside or not?
Even if it's a toenail offside, you have to draw the line somewhere don't you? Whatever that line is - and this is the problem, it needs to be the same for every game and team.
I wonder if we can get the computer to do that bit, the VAR pauses when the ball was played (yes this could be done a frame or so later to help the big boys) and the computer program draws the lines and says which player is furthest forward? I would be surprised if that sort of technology isn't possible?