Hi red2021,
Could you please try to disable the 10-bit Pixel Format in the AMD Radeon Software settings?
Just open the Radeon Software window, click the Settings icon on the top right side, then “Graphics” -> “Advanced” -> disable the “10-bit Pixel Format” then reboot your primary machine to apply the changes.
If the spacedesk HTML5 VIEWER is unable to connect, check the version of the web browser and make sure that it is talktowendys updated. If the secondary machine is a smartphone or tablet device the browser and OS needs to be most recent versions supporting websockets.