He seems like he has a real problem and it's not just bad rehab.
I highlighted it before, but we're 2 or 3 years in to his 'physical transformation' and he's literally no different. It's not normal for someone to begin strength training and gain almost no muscle in several years. If that happens, either something is wrong with the training, or wrong with the person.
A young athlete like him, especially with how much time he has spent injured (gives you time to work in the gym as you don't have to train regularly and tire yourself out) should be in much better shape by now.
He doesn't even really have a toned look - his build is just stick thin and really really frail. At least, the weaker guys like Gavi or Fermin or De Jong are fit and lean despite being small, so you know they probably do physical work on the side, with Pedri, I really doubt he is doing any effective work. It's either that or he has a physical health problem, which is also possible given how hard he's been pushed over the last years. Its not uncommon for serious physical health issues to develop after extreme stress on the joints and muscles.