Hide all (or some of them) your action bars easily. Enable CTRL/ALT/SHIFT modifiers to make them appear again (Default is only CTRL). Action bars reappear when your Spellbook is open. Optionally, when your Character or Talents panel is open.
Go to `Options Addons tab > HideMyBars` to change the settings. These settings are saved per character.
This works very well in combinations with large WeakAura settings, which can act as a fully dynamic UI. (example: https://wago.io/LuxthosEvokerDragonflight)