Hi @aLaw_ ,
A few questions:
- Are you running the latest Insider Preview? Even though the VHDX is older, it's best to enroll in the Windows Insider program from the Updates & Security menu in Settings, then upgrade to the latest build.
- If yes, Have you modified any group policy settings or made any manual settings changes to Windows Update? Usually these will cause problems with feature installation/updates.
- Do you have any proxies enabled on your system?
- When you go to install the .NET Framework 3.5 feature in the optionalfeatures program, does it give you an option to download the required files from Windows Update?