I'm not sure. I played only once the blackjack minigame and I won it.
yeah I played it a bunch to get some quick money if it was gonna be usefull, (it wasn't)
not yet anyway money is super easy to get and not useful at all.
but the dealer seemed to get 21 or at least beat me whatever I did.
I got 20 dealer 21 I got 17 dealer got 18-21 etc etc etc. So I assumed it was rigged machines to force you to lose money so you can trigger an event or something, but since you can just buy items for all your cash anyway it made no sense.
Eventually I just started winning by playing textbook blackjack so it was probably just unlucky. But there doesn't seem to be a point to the blackjack machines to exist yet.