Download Net Framework 35 Offline Installer For Windows 10 11 Free -

This method works 100% offline. You will need a Windows 10 or 11 ISO file (same version as your installed OS).

Final Recommendation: For a 100% offline installation on Windows 10 or 11, use Method 2 with your Windows installation media. This method works 100% offline

Fix: Use the DISM offline method (Method 1). It bypasses Windows Update entirely. Fix: Use the DISM offline method (Method 1)

The progress bar will go from 0% to 100%. Once finished, you will see:
"The operation completed successfully." The progress bar will go from 0% to 100%

Result: .NET Framework 3.5 is permanently installed. No internet required.