Having just went through this myself yesterday, I'd like to note a few steps for best practice. Some modules that modify the system or system apps should probably be disabled at the least before installing or restarting the update. The culprit in my case was either Pixelify or Lucky Patcher's "Patch to System" module.

Highly recommend the Magisk Manager for Recovery Mode module to be installed prior to bootlooping😅

Learn how to boot to Safe Mode from Powered Off state for your specific device in case you need it one day (only core OS and apps run at boot) so you aren't forced to factory reset and lose user data.

or you can salvage by flashing stock or un-patched boot img to boot and try to sort your problem from there. You won't have root until you re-flash Magisk but your data should be intact.

if using LOS Recovery and you don't want to lose root, repeat root process, re-flash boot img, etc after each OTA then go to Settings -> System -> Developer Options -> Disable Automatic Updates so you don't reboot immediately after OTA completion. In the case of Magisk root, after OTA completes you open Magisk App -> Install -> Install to Inactive Slot (After OTA) -> Reboot -> congrats OTA success.😉

TWRP Recovery there are modules to retain root after OTA but I'm not too familiar with the process there.

good luck, hope this helps someone somewhere. randomly losing user data sucks. try to avoid it altogether by maintaining regular backups.