This was actually an easy fix, all I had to do was to add a password into the "etc/shadow" file.
Here is a youtube video on how to do it:
https://www.youtube.com/watch?v=vyG1bMk522I
Here is the pic proof I logged into the Ubuntu 21.04 installer as root via UART Serial TTL:
I hope I can start the next process in installing ubuntu now...