I had this problem today morning with a newly installed 2019 server. it was working find until connect to domain.after joined to domain i cannot login to server with domain administrator account via RDP i just get a blank black screen.only task manager was working. after researching trying many ways this is how i manage fixed the problem

Change following setting in local GPO:

Computer Configuration->Windows Settings->Security Settings->Local Policies->Security Options

Enable “User Account Control: Admin Approval Mode for the Built-in Administrator account” which is set to “Not Defined”

After that do a gpupdate /force and try to login as domain administrator again