Thanks. Was able to update Manjaro-Arm GNOME Editon on USB Flash. But something interesting.
Update: Well so far the mainline linux 5.13.0-2 can reboot an shutdown cleanly on SD Card.
Somehow on USB flash drive the mainline linux 5.13.0-2, can only shutdown cleanly (i.e. does not need power cycle to restart/boot) but will Reboot into Android thus far (tried 6 times over the past few hours). And after reboot into Android, need a Linux on SD Card to regain the capability to boot again from USB Flash. Interesting. Will update if situation changes. With clean Shutdown is a good start.