Hello,
Please try the following methods to see if they work.
Adjust RDCMan Settings:
Modify the remote desktop settings within RDCMan to match your local resolution or enable fullscreen mode.
Use "Same as Client Area":
Select the "Same as client area" option in RDCMan to match the remote desktop resolution to your local client area.
Update Software and Protocol:
Ensure you have the latest versions of RDCMan and the Remote Desktop Protocol to resolve any compatibility or bug issues.