This seems so obvious, it's crazy this isn't being done everywhere.
Only somewhat positive example from the recent past is the Corona warning app: https://github.com/corona-warn-app
However I have met some truly brilliant people working for the city of Berlin. They're just limited by red tape and diffusion of responsibilities, not to mention the amount of work that needs doing.
Opening the code up to pull requests could give the city IT a free boost from motivated citizens, I think.