"But that would take local governments to sign up and developers / designers to begin solving problems that matter to their local society. Might be worth a shot though?"

Tech minds are always want to build a tool, not sure why it's just how we're wired.

Don't.

Just do less and do something.

Ask the "Head of Social Service & Care" you were talking to to get 5 or 10 colleagues to get in a room with yourself and a few other hackers.

Ask them their problems and write it all down. Then build something to solve ONE of their problems. This could be as boring as reducing their wasted time and money by automating a menial task in the departments offices.

Once you've built a thing show them it, then ask them to organise another meeting to talk about other problems. Ask them to invite community members. Then you do it again, and again.

Helping people isn't about building things, it's about talking to them about their problems and solving them. Keyword there "talking".