Why does Citrix CAG (RDP across monitors) take up multiple Spaces?
It sounds like you have it set to All Spaces [Desktops].
With the app running &amp; in the correct Space, right click it in the dock &amp; select Options &gt; This Desktop.

For a fuller answer on setting up &amp; using Spaces, see my other related answers at  https://superuser.com/a/1187552/347380 or https://apple.stackexchange.com/a/179403/85275