Commentators on ITV said it was a foul but outside the box therefore nothing.
Search brought up this
VAR review: This was a definite foul by Upamecano, who caught Kane on the back of his calf just has he was entering the area. But the VAR can only rule on the penalty and not a missed free kick. So, if the foul takes place on the line or in the area it's a penalty; if the foul takes place outside the area play continues from the point it was stopped.
This all comes down the VAR needing the weight of evidence to prove where the foul contact took place -- just like with the ball in play on Japan's winning goal against Spain. The VAR will take the moment of contact which causes the foul: where is that part of Kane's leg in relation to the line (the line belongs to the box, so it's a penalty if on it.) That Kane falls into the area, or has a foot inside it when contact is made isn't relevant.
The VAR will check every available angle (there are far more than we are shown on the television) to try to work out where this contact was, using multiple synced cameras to the same frame. The angles shown on TV really weren't conclusive, and only the camera square to the penalty area line can really give the VAR the best evidence. In this case, it was decided that contact was just outside the area, or at least there wasn't the evidence it was on the line.
But this again highlights the unacceptable level of information on VAR decisions from FIFA within games. It only shows fans what the VAR is viewing if the referee is at the monitor. Otherwise, it all goes on in the background and everyone is left to guess about the process. We all want to hear the audio from the VAR room, but at the moment FIFA (and UEFA for that matter) is reluctant to even show supporters what the team is looking at.