I'm pretty sure this is an actual bug with GCP at the moment. I'm the Organization Admin for the GCP organization (I've quadruple checked this, and that I'm signed in with the correct account).
But when I go to Manage Resources, And try to create a new folder, it doesn't let me select the organization as the location, because I "don't have the required resourcemanager.folders.create permission". If I try to create the folder in a project that's in the organization, I get "Unknown error".
I'm the user who created the organization and all projects in the first place, and the only G-Suite user that even exists on this domain.
If you review the permissions that Organization Administrator has, resourcemanager.folders.create is not one of them.
Org Admin by itself has almost infinite power because it can set IAM policies. This means the Org Admin can grant any IAM permission to any identity.
Grant yourself the required role such as roles/resourcemanager.folderAdmin.
Note: I recommend keeping the Org Admin as a separate identity that you lock away and only use to manage the organization. Create separate identities for day-to-day operations, development, and deployment.