More recently I developed a missing (in my view) extension to a piece of software. Too make this OSS-able would take a few extra hours and I wouldn't mind doing that step on my own time. But that's a nope.
So we can use OSS, we can modify OSS, but we can't contribute PRs or new software. At least for the three letter agency I work with. Lots of the type of applications being developed in the public sector aren't really any different then private sector. They take data in, they do something with it, and they output data. If the software doesn't require a security clearance, you should be able open source it IMO or at least contribute PRs.