My apologies about that. Let's try completely uninstalling .NET Framework and reinstalling it again.
• Press Windows Key + R to open the Run dialog.
• Type control and press Enter.
• In the Control Panel, go to Programs > Programs and Features.
• On the left sidebar, click on Turn Windows features on or off.
• In the Windows Features dialog, locate the .NET Framework entries (such as .NET Framework 3.5 (includes .NET 2.0 and 3.0) or .NET Framework 4.x).
• Uncheck the box next to the .NET Framework version you want to uninstall.
• Click OK.
• Windows will take some time to apply the changes and might require a restart.
Then, please download all versions and install them in this link.
https://dotnet.microsoft.com/en-us/download/dot...
Please keep me know if this worked for you.