Hey there!
Unless I'm not looking in the right places, Early Access currently does not have a "Hold Action" feature. It's a shame! I would really like that to be included in future versions of the game.
I also noticed that I cannot cast spells at a higher level spell slot than the spell itself. Which puts my Cleric in weird situations when I do not have a 1st level spell slot to cast Cure Wounds, yet my two 2nd level spell slots are just chilling, ready to be used. Would love to be able to cast lower leve l spells at different level spell slots!