Just out of interest, when you were running the line, how would you have judged someone offside? Presumably, movement was too fast to identify where feet were in a running motion or arms? Was it just the torso? And you couldn't be looking in two places at once, so did you listen for the moment the ball was kicked? Only asking because, how VAR determines offside, I would think, should follow the way linesmen do it, and, as far as possible, how fans see it.
Franky, I don't know how linesmen ever get offsides right, there is so much to look out and listen for.