Hi, thank you for the time you spent and excuse me that I'm responding so late. I worked on it last night but there was no success, I continued this morning and these are the results:

The key you suggested removed the certificate error, but another one appeared about verification of remote computer. I searched about it and found another registry key that removes it. No success, the window with progressbar appears, changes the message multiple times, goes away and nothing after.

So I searched more and someone mentioned that a graphic card driver update fixed their problem. It made me remember of that Chinese garbage that I could afford a couple of weeks ago, long story.

As a conclusion, now I'm totally convinced that something fundamental has gone wrong on this BAHAR-PC machine that it can establish an RD connection but it cannot keep it up and close it with no errors, so the source computer thinks "OK, that was it!". I search the event log on both machines and there was nothing there. I think it's not in the scope of my original question.

So back to 3 options you offered, now I stick to "connection from 1 to 2". Excuse my greediness that wasted your time. Then the problem is that FW disallows RDC again. I checked windows firewall and found that if I only disable Public Locations it will work.

Checking inbound rules I saw your rule up there which was enabled, thanks for the underscores! I filtered them to Remote Desktop and found the bastard. It was the "Remote Desktop (TCP-In)" which was disabled for Public profile.

@TroubleMakerChatBroom thanks again, I think I'm done, any security advises would be appreciated though. I'm waiting for your post to accept it.

@saastn Great, I'm glad you were able to get it resolved with some of the method we mentioned. I added the answer as I said I would with more detail and resources and links for further reading on the topics, settings, etc at the bottom of the answer.

I did just give a general breakdown of everything we went over with the troubleshooting methods I suggested though and worded it accordingly with notes, etc. to be sure to pick what works and be as restrictive as possible with the suggested troubleshooting methods.

Lastly, I added some security considerations as you requested as well but if you don't use this that often and you have the FW rule to enable or disable to allow the access, consider only enabling it when you want to use it. Otherwise lock it down some if you are on a large shared network.

If this is a small personal network that you trust every connected device to it, then you are likely safe if there's no one malicious connected to it internally trying to hack or brute force these systems and then RDP access.