I was curious about the app you mentioned and understanding how they solved the privacy & anonymity requirements.

This is the only similar app I could find but it’s not exactly as you mentioned. Can it be this one?

https://ijnet.org/en/story/yo-intervengo-mobile-app-will-empower-citizens-track-public-works-projects

If not I would be glad if you can share any reference to the one you mentioned. That would be really helpful.