Clara will recognize only the holidays that you either have blocked off on your calendar or that you've explicitly told Clara to block off (see this helpful article).
If you would like to proactively tell Clara which holidays you don't work each year, send Clara a list of the applicable dates (holiday name is not needed).
- Clara is not able to research dates of named holidays (e.g. you should share December 25, and not Christmas Day).
- Clara is not able to remember holidays year-to-year, so you should send the list each year
- Clara can read holidays directly from your calendar if you mark events as described here.