I doubt if the VAR could risk their job to that extent only to get match fixed, for them to be employed to do a professional service, they are expected to to condole any form of corrupt practice and if found, they are going to risk loosing their job, which i believe the consequence aftermath will be more higher than what they tend to be rewarded for fixing a match, maybe other people are doing such anyways aside the VAR.
The consequences are there for everyone, not only the officials, so whoever decides to be involved in fixing a match, whether it's a match-fixing or spot-fixing, basically takes the risk by taking the money and hoping that they won't get caught. So we can't say that officials who are in control of the game wouldn't be involved in fixing a match at all because money makes people do all sorts of things, especially if there's too much of it.
What fixers do when they are doing it in a big league or a world-class event is they do the tiniest things to make it look normal for others who aren't aware of what is happening and make their bets on those things. Or, they will do the type of fixing which cannot get caught. Imagine a team that tries very hard but can't score any goals. Anyone would say that they tried but it wasn't their day, and no one would think that the game was fixed.