Do you have DeX working via a KVM switch? If so, what brand of KVM and which DeX doc are you using?
DeX works fine on my Galaxy S9 DeX dock if I plug the HDMI cable and USB directly into the dock. But if I plug into my KVM switch, DeX mode comes on on the phone and the phone turns into a track pad--but the mouse and keyboard don't get power and the S9's HDMI signal doesn't reach the monitor.
I've tried re-plugging in to every alternate port on the KVM and on the DeX dock.
After a different problem mentioned here in the Community with a resolution problem, I uninstalled Samsung Smart Things app.
I am hoping for suggestion why the DeX dock works directly but not through the KVM switch and how to correct it. My KVM is an AV Access brand switch. The DeX Dock is a SkyWin. It charges the phone, the HDMI light comes on, but the keyboard and mouse don't work and the monitor stays blank. Thank you for any suggestions!