@Renee472 Yes, Instant Book doesn't require a host to accept, although they can cancel without penalties if something about the guest's communication or reviews sends up red flags.
Hosts who use Instant Book have settings where they can require that guests have some good reviews and have been recommended by other hosts, also that the guest has verified ID, so some guests won't have the Instant Book option available to them, like a brand new guest with no reviews, if the host has checked that requirement, which most IB hosts do.
Many hosts don't use IB at all. I require that all guests send a booking request- as a home share host, I wouldn't feel at all comfortable with a guest just being able to book without having the chance to communicate with them first to get a sense of someone I'm going to share my home with.
And I've also had guests tell me they wouldn't use IB, especially for a home-share listing, as they also want to get a sense of the host before committing to a booking. This is especially true of women travelling on their own, I've found.
And while lots of hosts love Instant Book, as it streamlines things and doesn't require them to accept or decline within 24 hours, some hosts have stopped using it as they found a lot of bad guests were coming their way and decided it was better to have a chance to vet guests a bit first, in case there were some red flags.