In Safari, you can press Cmd ⌘ ⇧ L to open/close the sidebar. When pressing this shortcut in Notes however, it creates a list.
What's the shortcut in Apple's notes app to toggle the sidebar?
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They don't actually call it a sidebar, they term it 'Folders'
It's in the View menu as Show or Hide Folders, with no default shortcut
You could make your own shortcut in System Prefs > Keyboard > Shortcuts >App Shortcuts - though you'd actually have to make two, for the different wording.
If you chose to re-use Cmd ⌘ Shift ⇧ L you would also have to reassign Checklist from the Format menu to something else before it will work.
Shown using a different key combo below for simplicity