There are several errors on VAR. Sometimes its use is totally unrealistic, sometimes its use is simply wrong. To be more specific:
OFFSIDE
In real life: VAR is called when a goal is scored with a possible offside position and you have 4 scenarios:
1) Linesman said goal, VAR shows offside, goal is disallowed
2) Linesman said goal, VAR confirms, goal is scored
3) Linesman said offside, VAR confirms, there is no goal
4) Linesman said offside, VAR shows no offside, goal is conceded
All these 4 scenarios happen in real football with almost the same frequency. In FM you only have 1