1. Right-click on the panel where you want to add the shortcut. This opens a menu for managing the panel.
2. Choose “Add new item”. This opens a window where you can choose the type of the item you're adding to the panel.
3. Double-click on “Launcher”. This selects the item type “Launcher”; it is used to simply launch any program, using a command line.
4. Type a name and description for your shortcut, choose an icon.
5. In the “command” field, type the command to open the desired directory with your file manager; e.g. “thunar /home/user123/desired-directory”. You may want to test the command first in a terminal.
6. Close.

A new icon should have appeared in the selected panel; when you click on it, the command you typed is executed.