External keyboard required. Without one connected, GarageBand on iPad is touch-only; none of these shortcuts are available from the on-screen keyboard.
Stage Manager menus. If Windowed Apps or Stage Manager is turned on in Settings > Multitasking & Gestures, swiping down from or moving the mouse pointer to the top of the iPad screen shows menus listing the available keyboard shortcuts, useful for a quick on-screen reference without leaving the app.
Left and Right Arrow do double duty. The same keys select the previous or next region in Tracks view, and separately step through instruments in the Instrument Browser, depending on which one is open.
One iPad-only shortcut. H shows or hides coaching tips, a shortcut Apple documents for iPad but not for iPhone.