It’s a “day of service”. Service to whom is another issue.
Personally, I say prayers that day for the victims, their families and for the 9/11 first responders who lost their lives and the ones alive suffering from disease/serious conditions. I refuse to go out and clean up a park or whatever. That is meaningless to me. I also educate my two youngest (11 and 5) why that day is a day for prayer and remembering. The significance of the event and what impact it made on Our Country and lives. That is my service.