On your web site: splashtop wired XDisplay needs to be uninstalled [it still installs an incompatible old legacy WDDM Filter Hook driver which cannot coexist with other similar products like spacedesk even though it doesnt even seem to use this old driver any more].
In Slashtops program, in the Advanced, section there is an option to install and uninstall their virtual display driver. If the virtual display driver is uninstalled then SpaceDesk works fine. There is no requirement to completely uninstall slashtop.
Help using Splashtop Wired XDisplay from techsupport