Your calendar shouldn’t get blocked for enquiries whether or not you pre-approve, decline or not; although you must respond with a message at least even if you don't decide if you will host the guest.
However, requests to book may block your calendar whilst the guest waits to hear from you/ if you do not decline or accept and the request expires, but you should be able to go into the calendar and unblock; the only time you can't unblock your calendar is when you cancel an actual confirmed booking.