Upgrading into RHEL9 failed with "Failed to isolate default target: Unit sysroot.mount not found." on boot

Solution Verified - Updated 2022-10-25T06:48:11+00:00 -

Issue

I'm trying to upgrade RHEL8 host into RHEL9 by following Upgrading from RHEL 8 to RHEL 9.
After leapp upgrade command completed successfully, the system was rebooted. But it failed with the following error during the system boot with the RHEL-Upgrade-Initfamfs grub entry.

systemd[1]: Failed to isolate default target: Unit sysroot.mount not found.

Red Hat Enterprise Linux 8

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