This Joplin auto open the current note in the Notebooks sidebar.
Basically this auto execute the joplin command focusElementSideBar (shortcut Shift+Cmd+S).
This functinalluty was missing and it exist in all modern IDEs (see for example vscode settings explorer.autoReveal)
After adding the plugin, you can toggle it form 'settings->plugin->Auto Show Active Note'
Side note
I would be happy to see this feature integrated in the main app branch instead have it in a plugin.