While i can select multiple files in the file manager by CMD-click on macOS, it's not possible to do so by CTRL-Click on Windows.

SHIFT-Click for selecting multiple files next to each other does work on Windows.

I have tested this
- on Windows 10 and Windows 7 machines
- on several installations of concrete5 8.4.2 and 8.4.3
- on different servers
- with different themes (including elemental theme)
- on a clean installation of concrete5 8.4.2 without any add-ons or themes installed
- with different browsers: Firefox, Chrome, IE 11, Edge.

Result:
It's possible to select a bunch of files next to each other by SHIFT + click.
It's not possible to select multiple files in the file manager by CRTL + click.

The second option is very much needed if we have to select files in order to be able to add them to file sets easily.