Forehand take back has a hitch (the unit turn is 2 pieces). Somewhat related, if his opponent plays straight up the middle to him he doesn't create adequate space. (He actually hits the FH pretty well on the run).
His serve...it's not how I would teach it, but I don't really see anything wrong technically. The year he won Bercy he was serving bombs.
He floats his slice backhand. No surprise, his (what, twice, three times?) former coach is teaching him 80's era technique here. As usual, PM has no idea what he's talking about. All modern players with a good slice finish across their body. (Tsitsipas also has a terrible slice BH, some coincidence that he's also a PM disciple).
Rune has solid technique on the 2HBH, IMO.
All of that said, IMO it cannot be understated that the vast majority of what is hurting him is between the ears, not how he hits the ball.