

If you pick a FOSS license then your project is FOSS. The number of developers doesn’t matter.
I moved all my (meager bullshit) personal projects to Codeberg awhile ago. My stuff was already open source, but I did explicitly add some license files I neglected to add before just to make it clear. So far so good.
Before you archive your Github repos make sure to update them with one last commit explaining that the repo has moved to somewhere else (and potentially why). Once you lock the repo you can’t make changes. If you straight-up delete them then this isn’t an issue.



To your point, here are two adjacent “parks” in Washington DC. The park on the left is fully open and walkable. The park on the right has a low fence and shrubs surrounding it. You could technically hop the low fence and walk there, lots of people let their dog do that so it can crap there, but both practices are discouraged.
Also, if you are mobility impaired, or its muddy, or whatever, you wouldn’t want to walk in the park on the left either. So it makes sense that OSM wouldn’t try to shortcut you over it.