Hi @cant94,
Using spacedesk Windows Viewer from Microsoft Store, you cannot select a custom resolution bigger than the machine’s native resolution.
However, using the desktop version of spacedesk Windows Viewer (v0.9.30 for Windows 7) downloadable from website, you can set a custom resolution up to 4096×2160.
Please keep in mind that when using the desktop version of the viewer app, some features are not updated anymore compared to features in Microsoft Store version.