It can’t be spent from**, yeah; it can still be “used” for holding funds while waiting though. Compared to P2TRv2 it’s added safety if the EC disabling event is delayed vs Q-day; compared to P2MR it’s fewer bytes on chain for the key-path prior to Q-day.
**Ignoring the possibility of using a high-fee to get a quick confirm of a key-path spend and hoping the quantum attacker can’t RBF/reorg your spend in the time between you broadcast your tx and it getting sufficient confirmations.