Node red is designed to use as little function nodes as possible. Sure, you can do anything with function nodes, but at this point, why use node red at all?
Look at sub flows, grouping flows and environment variables for sub flows, it will enhance what you can do a lot.
YouTrack can be self hosted. But it may be complete overkill. It has kanban boards, a ticket system, ganz charts, everything you might want.
But you don’t need to use all of it, it can be used in parts as well.
/edit: it’s not open source though, sorry…