If you tried to run a downloaded .NET 2.0 installer and received a "Not a valid Win32 application" error, it is because the installer you found was likely intended for 32-bit systems or is too old to recognize the Windows 10 environment. Use above instead, which ensures the correct 64-bit and 32-bit compatibility layers are installed correctly.
To enable it on a 64-bit Windows 10 system, you must activate the legacy feature through your system settings: Open Windows Features
This installs .NET 2.0/3.5 without internet access.