Apple trade in partner says my iPhone is jailbroken

Recently I traded my iPhone 12 pro max for 13 and when I sent my device back to trade in partner, I got an email saying that apple will offer me $0. I was shocked and tried reaching out to apple support. Then they revealed me that my iPhone is jailbroken and because of that reason, they couldn’t give any value to my old device. As far as I know, I never ever made alterations/modifications to my device. Can someone jailbreak my device without me knowing?