Yay, I got it. I went to this web page: https://help.content.samsung.com/csweb/faq/searchFaq.do And found these instructions: Disconnect and then reconnect your USB cable while Samsung DeX for PC is running on your PC. Once your mobile device is recognized by your PC, a "Samsung DeX is connected." message will appear in the notification panel on the mobile device, and then the Samsung DeX Home screen will appear on the PC screen. If you can't see the Samsung DeX Home screen even after reconnecting the USB cable, try the following: - Reinstall the USB Driver on your PC. ▷ USB Driver installation directory on a Windows PC: C:\ > Program Files (additional characters, such as "(x86)", may follow depending on the system) > Samsung > Samsung DeX > USB Driver > SAMSUNG_USB_Driver_for_Mobile_Phones.exe ※ A USB driver for Mac is not provided separately. - The driver may not run immediately after installation. In that case, restart your PC. - If the USB cable or hub is damaged, you may not be able to connect. Try a different USB cable or hub. ※ If Samsung DeX does not work correctly on a PC running on Qualcomm's Snapdragon platform (Windows on ARM), we recommend that you connect the PC through a USB hub instead of connecting it directly using a USB cable. - Check the USB option through the notification displayed on your device. Then, select "This phone" for the "USB controlled by" option. - Check whether the "Samsung DeX" icon is on the system tray of the taskbar. If you don't see it, run the "Samsung DeX" program. If you see the "Samsung DeX" icon, reconnect the USB hub or cable. ※ PCs within a company and public PCs typically have their own security software installed, so you may be unable to connect to them via USB. If you can't connect to a PC via USB, contact the administrator of the relevant PC I ran the SAMSUNG_USB_Driver_for_Mobile_Phones.exe and re-installed the drivers. That didn't help, but I rebooted the PC and then I think it took. When I next plugged in the phone, the app auto launched and the red exclamation points were now spinning circles and then it connected. Cool. And... I just realized Dex recognizes my touch screen gestures too. Very nice.
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