@Filomena57 Airbnb doesn't tell you this, but there is no need to ever decline an Inquiry. An Inquiry message only needs to be answered by messaging back the guest within 24 hours. You don't need to click on Pre-approve or Decline. So never waste a decline on an Inquiry, just let the inquirer know why it isn't possible.
You will get pesky messages urging you to pre-approve (because Airbnb wants you to accept every guest, no matter how rude or sketchy), but you can safely ignore those, and if you clear your cache, they should disappear.
Of course, a Booking Request is different, you do have to either Accept or Decline within 24 hours, but if the request is inappropriate, messaging the guest before that time is up, saying why you can't accept and urging them to withdraw the request so they don't get charged, can sometimes work and save you from having to decline.