By default, RDP access to a server or client is always disabled and needs to be turned on manually. In a domain, you can use a group policy to enable it via GPO but there are several settings to be configured before it works. If one is missed, you may end up with the Enable Remote Desktop slider set to off and grayed out:
Configure the following items in a group policy to properly enable Remote Desktop access:
Computer Configuration → Policies → Administrative Templates → Windows Components → Remote Desktop Services → Remote Desktop Session Host → ConnectionsAllow users to connect remotely by using Remote Desktop Services = Enabled