You will most likely not want clients to book out time with you on public holidays. But it's also time consuming for you to block out public holidays one by one for each location.
In order to block out slots for public bookings over the course of the year, you can subscribe to external calendar feeds for holidays for the country you are based in.
Then go to each team member you'd like to subscribe to this calendar, and add the iCal import url as you would for any external calendar:
After saving these settings for each team member, their calendar will now have public holidays blocked out on their calendars.