I'm pretty sure if it hits a body part and then the arm it should never be given as a penalty, and that was a rule brought in a couple of years ago, but tbh I don't know what the rule is anymore. I think it's basically whatever the group of officials decide at the time.
Youre correct.
Why De Ligt didn't warrant a penalty
by Football Italia36 minutes ago
Bologna had penalty appeals in the final minutes of their 2-1 defeat to Juventus, but the IFAB rules show it was not a spot-kick.
The incident occurred in stoppages and there was a ‘silent check’ in the VAR booth, alerting the referee he could continue the game.
Fans were furious, but a look at the 2019-20 IFAB Laws of the Game shows why De Ligt’s intervention did not warrant a spot-kick.
The Juve defender slipped as he went to clear a cross, it bounced off his foot and on to the elbow that was placed behind him.
This is not a penalty for three different reasons:
The following will not usually be a free kick:
The ball touches a player’s hand/arm directly from their own head/body/foot or the head/body/foot of another player who is close/near
The ball touches a player’s hand/arm which is close to their body and has not made their body unnaturally bigger
If a player is falling and the ball touches their hand/arm when it is between their body and the ground to support the body (but not extended to make the body bigger)