Remote Connection Desktop Manager 2.7 does not support dpi scaling anymore?
To clarify where to find this checkbox, go to the actual .exe file in C:\Program Files (x86)\Microsoft\Remote Desktop Connection Manager and right click the .exe file and click the Compatibility tab.
2018 Windows 10 Update (1803/1809)
There are new cascading dialogs as shown below
RDCMan.exe --> Properties --> uncheck “Disable display scaling on high DPI settings”.