Jeremy Crawford on X: A readied spell's slot is lost if you don't

spell slots you have to cast your wizard spells of 1st level and higher To cast one of these spells, you must expend a slot of the spell's level or higher

A readied spell's slot is lost if you don't release the spell with your reaction before the start of your next turn

spellcast slot With these Spell Slot Trackers you have the number of open spell slots for your caster always in sight

spell slot counter You don't have to rest when you use all of your spell slots They do have a mana system It's the spell slot system You have multiple pools of