CH340 / CH341 USB Driver
Some Arduino Nano clones use the CH340 (or CH341) USB serial chip. Install this driver on your computer so mBlock can talk to the board.
Windows
Download and run the installer.
Mac
Unzip the file and run the installer. May need to allow in System Preferences.
After installing the driver, reconnect the USB cable and open mBlock. If still not visible, try restarting your computer or see the Connect Arduino page.