I do believe casinos and any electronic gambling game is rigged, and I guess they have to be, but it just depends on your interpretation of the word I guess. As far as I know, when you click spin a number is chosen from the RNG and that number is then used to lookup a win/loss in a table of pre-determined results. That means that there are some combinations of reels that cannot appear on the screen, because only a finite amount of combinations are held in the table. To me, that is the same as being rigged. And when you play roulette, it is not picking one number, but 5 or 6 and then deciding which one to use depending on the outcome of the RNG, and that is not how ‘real’ roulette works, so again to me that seems rigged.
And I do believe that there is a way that a casino could give a streamer an unfair advantage if they wanted to. Nothing is impossible.