What device do you have.? (EDIT NVM, I seen it's a 4 XL). Anyways since your device isn't a pixel 5a 5g or newer, you don't need alpha/canary magisk to root A12. I'm using the 4 XL rn with stable magisk (23000) on A12 November security patch. Try stable magisk since you're not on a pixel 5a or newer and report back. I also did an OTA from A11 to 12 without any issue. Same modules for me etc so it might be a magisk canary/alpha issue.