Hello William,
Thank you for posting question on Microsoft Windows Forum!Based on the issue description as well as the provided error 0x3 with extended error 0x410 with the Remote Desktop Connection Broker (RDCB) being unable to validate the settings in your RDP file which might point to issues with the RD Connection Broker service or configuration on the server side.
Since the RD Connection Broker service (tssdis.exe) might have stopped or failed to start after a reboot or update. The suggestion is to restart core RDS services, such as Remote Desktop Connection Broker service and Remote Desktop Services . If it is not running, start it manually. Also, set its startup type to Automatic to ensure it launches on boot.
Another suggestion is to verify group policy configuration. Any incorrect or missing Group Policy settings for the Connection Broker name can cause validation failures. Open Local Group Policy Editor. Then navigate to this path Computer Configuration > Administrative Templates > Windows Components > Remote Desktop Services > Remote Desktop Session Host > RD Connection Broker. Making sure that the Configure RD Connection Broker server name policy is Enabled and points to the correct broker server FQDN. If you have a domain, verify the same settings in your Domain Group Policy.
On the other hand, a corrupted local RDP file can trigger this error. Try to recreate the RDP connection file by opening Remote Desktop Connection (mstsc). Enter the server address and configure your settings. Do not save over the old file. Instead, create a new RDP file and try connecting with it. Also, it is worth using the /admin switch to connect. This will bypass the Connection Broker and connects directly to the session host. Type mstsc /admin, and press Enter. Then enter the server address.
Hope the above information is helpful!