Updated: Dec 26, 2020
I've already done it, so why not share it? This google sheet lists US and Mexican holidays, World holidays, solstices, New Years dates, monthly themes, the beginning of religious holidays (Catholic, Hindu, and Jewish) along with any official hashtags. Available to anyone/everyone.
Would you like to add the holidays for a country or culture? Let me know which at firstname.lastname@example.org and we'll arrange access.