Could you please try the following on your primary machine.
- right-click C:\Windows\Temp folder -> Properties -> Security tab -> Advanced -> Permission tab -> Continue
- check if you find the Users or Authenticated Users and make sure it has Full Control access
If none, just Add -> Select a principal, then type "Users" and click Check Names and click OK
- Then make sure to check the Full Control access for the Users then click Apply -> OK.
After following the steps above try to run-install again the spacedesk MSI installer.
Looking forward to your feedback.