Does the viewer app shows display off status or black screen upon spacedesk connect?
Did you connect spacedesk over wireless network? or USB tethering or WiFi Direct?
Did you notice any error notification on your primary machine upon connection attempt?
To further analyze this issue, please download the spacedesk diagnostic script here, then extract it.
Inside you will find spacedeskDiagnosticTool.cmd, just right-click it then run as administrator.
This script will start a debug view app to capture spacedesk debug traces.
On step 5 it will prompt you to reproduce the issue (by trying to connect the viewer app and wait for the issue to happen), make sure to do this before pressing any key to continue.
After the script is done, a folder will be created on the same folder as the script file which contains various log files that we need for analysis.
Please right-click it -> Send to -> Compressed (zipped) folder, then attach the *.zip file on your next reply.
PS: Attach option should be visible on your side after your second post.