What are the modern-day requirements for this Jewish High Holy Day?

Reform Judaism typically prefers the term High Holy Days over High Holidays because the former emphasizes the personal, reflective, introspective aspects of this period. By contrast, Holidays suggests a time of communal celebrations of events in the history of the Jewish people.[citation needed]

Explanation:

geography

this is because warmer climates often don't get people sick from the flu and regions where it was often colder more people received the flu. hope this if you need more reasoning i am here to