To allow a Remote Desktop connection, in the client side can be use Remmina and in the server is mandatory enable the Remote Desktop option, it through Settings → Sharing. This GUI is the same for Ubuntu and Fedora.
In the bottom of the Remote Desktop window exists the Authentication section and the Verify Encryption button. If it is press it appears a small window with the Encryption Fingerprint value - it in the server side. For the client side - this value appears for the first attempt connection as a Certificate. Is mandatory accept that Certificate to accomplish the first connection and make others in the future.
Just being curious, for security reasons, is there a way to regenerate or create a new fingerprint?
Consider the case if exists 3 remote clients (does not matter if is the same person or not) and the laptop/PC of one of them was either compromised or stolen. Yes, I know that can be changed the User Name and Password, but to increase the security is possible change or recreate/generare a new Fingerprint?
Thanks again for the quick and polite reply - valuable your support. Let me do a research about that command and once confirmed, I am going to mark you answer as the solution.
In order to generate a new crtificate/key you could also use winpr-makecert -rdp -path /var/tmp/
(winpr-makecert command comes from the freerdp package).
If the RDP client machine is stolen or compromised, change the RDP credentials on the server.
Note that regenerating the server’s key or certificate does not provide any security benefit.
If the RDP server machine is stolen or compromised, remove its certificate fingerprint from the client.
You can also regenerate the server key and certificate by resetting the relevant settings and then toggling remote desktop sharing in GNOME Settings: