Some features of the Duet software need network access to work properly. This article describes how to change the firewall settings in Windows 10 to allow the Duet app to have network access.
Start by clicking Settings on the Windows start menu.
When the Settings window appears, type the word firewall into the search box near the top of the window.
In the list of search results, click Windows Defender Firewall.
When the firewall control panel window appears, click the item on the left labeled Allow an app or feature through Windows Defender Firewall.
When the list of apps appears, click the Change settings button in the upper-right corner.
Scroll through the list of apps until you find the entry for Duet Display. Make sure all three checkboxes are checked, as shown in the picture below. Click the boxes to check any that are unchecked.
When finished, click OK to finalize the changes, then close the control panel and Settings windows.
The changes are applied immediately. Restarting Windows is not necessary to update firewall settings.