I’ve seen several people in tags saying that Magnus acted OOC in the scene with Izzy, and that he should’ve done something to prevent her from going on search for yin fen. But like… He did what he could? He scared off that Rufus drug dealer away, he approached Izzy as a friend, warned her about how dangerous yin fen is. Yet, in return Izzy, being under the drugs infuence, turned a full “holier-than-thou” Shadowhunter mode on him, and on top of that dropped Aldertree’s name. Obviously, that was the drug talking, rather than Izzy, but what could Magnus do in that situation? It’s his, the downworlder’s, word against the word of a shadowhunter. He had no real proof, save for his hunch. Even Alec might have not believed him. Not to mention that Aldertree tortured Raphael just a few days ago.
The way Magnus says “Apologies” – his whole body language shows subordination. No matter how old, wise and powerful Magnus may be he’s still a downworlder, and Izzy’s a shadowhunter.