You can uninstall Magisk from the Magisk app, as Update needs stock kernel. Download 126.96.36.199 update from Oxygen Updater app and install from Settings/ update from local storage. Do not reboot, then Install Magisk to Inactive Slot. Now you can reboot. Then use kernel manager to flash Kernel.
Yes when updating using a FULL OTA. When was the last time a FULL OTA was on time and not a month or two late. You can not take an incremental update on Omega or any custom kernel. It will fail.