I am running Linux Mint 19, and I would need the system to avoid opening any windows when I plug in a USB drive. I can't seem to find anything in the System Settings to configure this behavior. I have also Googled and not found nothing relevant. Would you please advice?
The default behavior of Linux Mint is to automatically mount the disks. I believe the options you seek to disable this feature, are located in Nemo preferences >> behaviour tab.
Open Nemo, click 'edit' at the top, then select 'preferences' at the bottom of the drop down menu. If you then select the behaviour tab then uncheck "automatically open folder for automounted media".