I just installed the full OTA via Local Upgrade in System Updater. And b4 reboot after installing, i used the "install to inactive slot after OTA" option in Magisk Manager.Did you have to patch the boot .img from the new 11.0.6.8 OS, and I noticed on the upgrade flash you did the "install to inactive slot after OTA" according to your post.
Patching the boot.img is just needed the first time gaining root.