Why doesn't the VAR get used at corner kicks, very often the ball is outside the semi circle, should a team score from the corner kick, should it be allowed
For a corner kick the ball does not have to be within the arc of the corner. The ball simply has to break the plane of the arc for it to be in a valid position. So it can be outside the arc, and 1mm of the ball overhanging the white line of the arc and it will be valid placement. See here.
The reason I believe why VAR would not be used for this because it is a very minute offence should be ball not be breaking the plane of the arc. If VAR was used corner kicks, it would then have to be used for the EXACT placement for free kicks and goal kicks also (where the same rule for breaking the plane of the line applies).
So yes, the goal should be allowed to stand.