Thanks.
Into which folder do I have to place the ISO file for Flight Simulator to find it?
As you can see you are dealing with a layman, sorry.
The location does not matter. You can let the iso in any folder, even on a shared folder from a NAS or from an USB flashdrive, your desktop etc...
The only thing that matters is to launch the iso by double clicking, and then it will be automatically mounted as a new drive with a new letter.
for convenience I let the iso file in the same folder of the game and put a shortcut to my desktop.