Hello.
1) Yes, it’s possible, of course.
You can add the block bookings at the Booking > Add booking page in Admin panel (or at front end side booking form).
Watch it in this video guide https://wpbookingcalendar.com/help/add-new-booking-admin-video-tutorial/
2) If you do not see the booked dates in calendar at the front-end, please open the General Booking Settings page and in the “Advanced section”, please be sure that you have not activated this option: “Allow unlimited bookings per same day(s):”. This option must be unchecked. If its checked, please uncheck it and update the settings.
Also this option “Use pending days as available” must be unchecked, as well. It’s located at the Booking > Settings General page in Advanced section.
If you still will have this issue, please recheck for the any cache plugins, like “WP Super Cache” or “W3 Total Cache”. If you are using someone, please deactivate it or add the exception to the page with booking form for do not cache this page(s).
Kind Regards.