To add, if I'm not mistaken, online casinos' RTP on both DEMO and ACTUAL slot can be different, in which they add more RTP on the DEMO mode. Not sure if it's absolutely true, my experience on both gambling with real money and playing demo modes, in demo, I'm winning a lot. So I guess it is somewhat true.
RTP on DEMO & ACTUAL slot
SHOULD be the same. For an obvious reason, player should experience the same play on free play and real-money mode. Otherwise, it's not a fair deal to player. But, yeah, I have seen sample of a different RTP for a free & real money mode.