Yes, you need to mark bank holidays as unavailable in your Calendar if you will not be working on those days.
Bank holidays are not automatically blocked out, as not all therapists are based in the UK, so public holidays are not universal across all therapists on the Platform.
Some UK-based therapists also choose to work on these days as we do receive bookings on bank holidays (including Christmas, New Year, Easter etc.), so it is your responsibility to ensure you update your availability to show if you will or will not be available for bookings.
You can find instructions on how to update your unavailability here.