We used the following reg key to hide the start menu in windows, and then we turned off the setting “hide start menu” setting within appcenter.  This allowed Citrix to take over the fullscreen.

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Shell\OnTop]

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Shell\OnTop]

"Default" = dword:00000000

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Shell\AutoHide]

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Shell\AutoHide]

"Default" = dword:00000001