You literally get the software, you drop the Newsflasher software in the update folder after connecting your phone via fastboot or recovery, voila
It unroots after updating, but to fix it, after the update, you unsin the vendor image with magisk, flash the magisk vendor image - root is back
You lose no data unless you use the wipe command. Only reason it happens initially on first root is since you unlock the bootloader, it has a defense mechanism if you may (to protect user data). After this, you can just apply the new software and keep your data moving forward.