In the Notes app on your Mac, you can quickly accomplish many tasks using keyboard shortcuts and gestures. See the shortcuts and gestures on the linked page, as well as keyboard shortcuts in Notes menus in the menu bar. In app menus, keyboard shortcuts are represented by symbols.

Note: Keyboard shortcuts in apps may vary depending on the language and keyboard layout you’re using on your Mac. If the shortcuts below don’t work as you expect, look in the app menus in the menu bar to see the correct shortcuts. You can also use the Keyboard Viewer to see your current keyboard layout, known as an input source.

See https://support.apple.com/guide/notes/keyboard-shortcuts-and-gestures-apd46c25187e/mac

Addendum (from John C):

On the iPad with an external keyboard, if you hold down the Command key, then a list of unpublished shortcuts show up. The two that I like to use a lot are:

Collapse all Sections: Shift>Command>Option>Control>Left arrow

Expand all Sections: Shift>Command>Option>Control>Right arrow

Without the Shift key, it works on just the current selected Section.

A Section is any paragraph that is assigned to be a Subheading or Heading.

Collapsing a Heading hides all Subheadings below it up to the next Heading.

What I like to do in Notes is to assign “Subheading” to a date or a subtitle, then below that, enter my note. Using the keyboard shortcuts above lets me collapse or expand Sections as needed. This greatly assists me in accessing a given Section.