Investinlibraries.org/ has a sticky note wall where people can post how the library has helped them. I don't know how much this is being seen by the city government right now, but I know it's been used in previous funding efforts (e.g. on NYPL's front page). There's also testimony that was used in budget hearings in May 2022.

Also, just spread the word! Check out books from your local branches, register/RSVP for events and classes, take advantage of as many services you can from NYPL, BPL and QPL. Stats should (in a perfect world) count for something in these decisions.