Ethiopian Jewish holiday occurring 50 days after Yom Kippur

https://www.hebcal.com/holidays/sigd-2021?utm_source=js&utm_medium=icalendar

Beginning of new Hebrew month of Kislev. Kislev is the 9th month of the Hebrew year. Corresponds to November or December on the Gregorian calendar

https://www.hebcal.com/holidays/rosh-chodesh-kislev-2021?utm_source=js&utm_medium=icalendar