Face ID
Hello customer support! I own an Iphone 12. After resetting the settings, there was a problem with the face id, my younger brother, who is 12 years younger than me, can unlock my phone. We can attach a video to this.
iPhone 12, 14
It is likely Face ID thought your brother was you, you could try setting up Face ID again, if that fails you could hope that over time Face ID can learn about your appearance (as it can if you grow a beard, or start to wear glasses or begin to wage), or you could stick to using a passcode.