Allow Domain Users To Login To Server 2016

You have to create a domain group inside your domain controller users and computers management and then add that group to remote desktop users and wise desktop users and then add in all those domain users that you want into that group so that they can login,

Then go into the policy manegment and navigate to security and user rights (under windows and local policies) and select
RDP - Allow log on through Terminal Services to allow also that new domain group you created! there you go simple test it out

2 sources:

social.technet.microsoft.com/Forums/sharepoint/en-US/c8709b32-e950-4299-b1a5-704285dee7b1/allow-normal-user-to-login-to-domain-controller?forum=winserverDS

woshub.com/allow-non-administrators-rdp-access-to-domain-controller

Also as an extra bit of vital info, you will need to use the domain names name / hostname to rdp and not the IP as IP's can be spoofed and windows server 2016 has stopped IP's just being used!