I've never heard of it, but good for them...
Mark your calendars! Americans to get new holiday thanks to groundbreaking January 1 law
https://www.the-sun.com/news/15690994/new-holiday-groundbreaking-law-california-diwali/
.... .. California declared that Diwali will be officially added to the state holiday calendar in 2026. The state is home to roughly 960,000 Indian Americans, which makes up about 20% of all Indian Americans in the country.
The festival of lights changes dates year to year, and next year it falls on November 8. Since November 8 is a Sunday, Americans will observe the holiday on Monday, November 9. .. ... The bill authorizes public schools and community colleges to close on the holiday. Plus, state employees are allowed to take the day off. .... ...
Connecticut and Pennsylvania are the only other states in the country that mark Diwali as a state holiday.
Diwali is celebrated in Hindu, Sikh, Jain, and some Buddhist cultures to mark the triumph of good over evil, light over darkness, and knowledge over ignorance, as well as to honor goddess Lashmi and Ganesha.
The Bay Area is home to the largest Diwali celebration on the continent. The area, which comprises Alameda, Contra Costa, Marin, Napa, San Francisco, San Mateo, Santa Clara, Solano, and Sonoma, hosts major festivals every year to celebrate. .... ..
https://www.the-sun.com/news/15690994/new-holiday-groundbreaking-law-california-diwali/
It's big here in the greater Vancouver area of British Columbia (but no holiday, unfortunately).