When you use the word need it seems like you’re asking if a certain number is required. Community service is not a requirement to apply to Harvard. Having said that all of these types of schools want to know how you spent your time during high school. Some folks worked. Some did community service. So played music. Some built weather stations and nuclear submarines (I kid) and some did all of the above all at once… but you’re asking what’s needed to apply and zero is the answer.