I wouldn't use anything but water.
The info is probably out there, but the long term effects of most other things aren't commonly known.
Professional conservators use a variety of things specially made for that sort of work, but if you can't afford a homemade formula the professional stuff isn't in your future.
Vinegar is an acid, and with already acidic cardboard I'd expect it to make any degradation worse, especially over time.
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