When citrix receiver is fullscreen, Alt-Tab and any other hotkeys are forwarded to the server instead of being interpreted on the client.
One can use the mouse to access the citrix menu top middle on the screen to switch the citrix receiver window from fullscreen to a window and then use Alt-Tab to change keyboard focus to another application on the client PC, but this is tedious.
I'm looking for an easier way to switch from citrix receiver to another client program with a keyboard combination (hotkey). The citrix receiver user's manual does not tell anything about the keyboard.