They used to say that Bitcoin COULDN’T be hacked...
Self-custody bitcoin where you transfer it from an exchange to your personal hardware wallet can't be hacked unless you tell somebody your key.
Bitcoin exchanges can be hacked, because a bitcoin exchange is just an online bank that stores your bitcoin. You don't really own it when you leave it on the exchange. It's just a bitcoin bank account that credits your assest in bitcoin instead of dollars, and banks can get hacked.