Windows : workaround for "impossible to install .NET Framework 3.5"

On Windows 10 or 11, when running an old software, you may be faced with the following error indicating that you must install the .NET Framework 3.5:

You can of course let Windows download and install the framework but, in case it fails, here is another solution:

• Make sure you have a version of Windows 10/11 :
• ISO files can be downloaded for free on the internet
• You can mount your ISO file on a virtual reader, with software like WinCDEmu

• Then go to command in administrator mode (type CMD then right click and "execute in administrator mode").
  
  
• Enter the line below (by replacing H: by the letter from your virtual reader). It will activate .NET Framework 3.5 using specified sources files, without connecting to the Internet to download the files.
  dism /online /enable-feature /featurename:NetFX3 /Source:h:\sources\sxs /LimitAccess
• Wait during installation (this may take several minutes).
  
  
• At the end of the operation, your system should have the 3.5 framework and the initially blocked software must start as in the past.