Puzzled myself.

Edit: did a search, and I’m guessing this one: https://en.wikipedia.org/wiki/Assumption_of_Mary

Probably a holiday only in Catholic countries, and very likely not in protestant ones.

Relevant map (no valid source, just took the first image from DDG):

Checks out, more or less: https://www.axa-schengen.com/en/blog/holidays-europe-country