Before I begin, I am experiencing the same problems on the Github issue: https://github.com/topjohnwu/Magisk/issues/4343 and coming here for further support & starting a new topic on the same issue here.
I have successfully applied the Android 12 update fine, no bootloop, no brick, everything is still here with my data intact. Because I am applying a system update and would like to still have root without wiping. I tried to apply the magisk patch thru the boot.img and every time I try to apply the patched boot.img the error "failed to load/verify boot image" pops up and cannot proceed further. A user on the issue said you can use these steps to boot the phone, while this does work, every time the phone reboots the steps must be completed again. Is there any way that I can fix the "failed to load/verify boot image" without wiping everything on the phone & keep everything or do I have to wait for an update? Thank you.