Main monitor for the Remote Desktop Client

DBR14 

I've found a way to select the main display.  

Background:

With mstsc.exe, which is clearly the basis for this new AVD Remote Desktop application, selecting the main monitor involves editing the .rdp file's selectedmonitors setting.  

Example

selectedmonitors:s:2,1,0

The above setting will make monitor #2 the main monitor as it is listed first.  

The same settings seem to be used for the new remote desktop app, but they are instead stored in the Windows Registry

HKCU\SOFTWARE\Microsoft\RdClientRadc\Feeds\<account_email>\<feed_ID>\DesktopDisplaySettings\<machine_ID>\SelectedMonitors

Of course, you will need to determine the <account_email>, <feed_ID> and <machine_ID> for the specific connection you are trying to modify.  Once you locate it, just modify the order of the selected monitors and reconnect to the AVD.