And there's also some civilian restrictions on flying and other aviation related things, including flight and duty time. But to say you can't do anything whatsoever "on the side" is completely unenforceable and so broad its slam dunk lawsuit material if even attempted.

The mil/USERRA issue is currently being challenged and I think they will probably prevail at least to some extent. But either way that's nowhere near a total and complete fantasy ban on 100% of all "side hustle" gigs.