The people who seem unbothered are sometimes just better at keeping the noise inside.

Calm on the outside is not a readout of the inside. Some people genuinely have low weather. Others have learned to keep it from showing, often because showing it once went badly for them. From where you are standing those two look identical, which is why the steadiest person you know can be the one carrying the most.

Stop using composure as proof that somebody is fine. Check on the person who never seems to need it, in a low-key way: a walk, a lift home, a message that does not demand an answer. And notice when you are the one performing calm, and who you could let see otherwise.