Hello @Michal Detko ,
Thanks for your query.
1.Please try to change Security of RDP in Group Policy Editor
Go to the Start Menu, search for Local Group Policy and open up ‘Edit group policy’.
Navigate to the following directory:
Computer Configuration > Administrative Templates > Windows Components > Remote Desktop Services > Remote Desktop Session Host > Security
On the right-hand side, locate the ‘Require use of specific security layer for remote (RDP) connections’ and double-click it to edit it.
If it is set to ‘Not configured’, select Enabled and then in front of Security Layer, choose RDP.
Click Apply and then hit OK.
Restart your system so that the changes take effect.
Try connecting again.
2.Try the solution to change the IP address of RDP server, and of course the client you are using.
https://learn.microsoft.com/en-us/windows-server/remote/remote-desktop-services/clients/change-listening-port
Best regards,
Leila
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