CAB files for .NET Framework 3.5 can be downloaded from various sources, including:

You won't find a direct "download" button for this CAB file on Microsoft's website. Instead, it is tucked inside the Windows Installation ISO. Mount your Windows ISO : Right-click your Windows 10 or 11 ISO file and select . Note the drive letter assigned (e.g., Navigate to the source D:\sources\sxs Find the file : Look for microsoft-windows-netfx3-ondemand-package.cab