I stopped using the Mac RDP client long ago, and I only use Remmina from a Fedora box to use RL boxes via XRDP and the Windows RDP client to talk to Windows servers, but I found something that could be useful at:
An excerpt:
Use a keyboard in a remote session
Mac keyboard layouts differ from the Windows keyboard layouts.
- The Command key on the Mac keyboard equals the Windows key.
- To perform actions that use the Command button on the Mac, you will need to use the control button in Windows (for example Copy = Ctrl+C).
- The function keys can be activated in the session by pressing additionally the FN key (for example, FN+F1).
- The Alt key to the right of the space bar on the Mac keyboard equals the Alt Gr/right Alt key in Windows.
By default, the remote session will use the same keyboard locale as the OS you’re running the client on. (If your Mac is running an en-us OS, it will be used for the remote sessions as well.) If the OS keyboard locale is not used, check the keyboard setting on the remote PC and change it manually. See the Remote Desktop Client FAQ for more information about keyboards and locales.
Using Remmina, doing copy/paste requires using ctrl+shift+c to do copy and ctrl+shift+v to do paste in Terminal. It might be a preference setting in the MS RDP client.