Hi, I followed exactly the procedure in the link above and I got no error message. I use Magisk 25.2 (hidden).
After having the boot loop I started in fastboot and switched the the other slot (in my case b) and restarted successfully without root and without the OTA installed. So I ran the update again and rebooted after that unlike in the original instructions. The I boot via fastboot into some recovery (LOS or TWRP), run dd to get the boot.img and re-root from scratch (first patch the extracted image, boot it via fastboot and the install Magisk directly.
Is there a way to check the two slots for inconsistencies? A hardware issue should produce other problems, too IMHO. And after the second OTA run a is active (before it was b) and it booted successfully so I doubt that there is a hardware problem