This happened to me as well with a secondary iCloud account, and I still have no idea what triggered the ban. Apple support said they couldn't reverse it. The account was on an old iPhone, and after the ban, it became impossible to log out, rendering the device e-waste overnight. I at least didn't have any valuable data in icloud. But that experience prompted me to stop using Apple products or any other device that requires an online account to function. Fortunately, since recent AMD APUs are quite capable, I sold my MacBook M2 Max and have happily returned to using x86_64 Linux. No more Apple in my life, ever.