I installed from this source and Greenbone is working but Im wondering if I can run the Greenbone OS Administration or not. https://www.mikeslab.net/install-greenbone-vulnerability-manager-20-08-on-ubuntu-20-04/
First welcome here,
I would suggest you read the FAQ first:
Greenbone OS is exclusive to our (virtual) appliances, so no administration like the GUI and ansible is possible.
Never the less you can still use GMP to automatize the vulnerability management process, but not the GOS administration.