By design, all slots are “rigged” to provide a house edge to make the casino money. Over time, they will pay out less money than they take in. Slot designers often program near-misses to make players feel as if they “just missed” a big payout. Their randomness is what makes them fun. You never know when or how much of a payout is coming.
For every state with legal online casinos, there will be some sort of gambling regulator that will test and check that no legal casino has rigged the games in an unfair manner. All return-to-player percentages are verified and published.