RTP estimates long-run returns; the house edge is the casino’s average share....

https://www.quantifiedstrategies.com/rtp-variance-and-expected-value-applying-a-quantitative-framework-to-online-casino-gaming/

RTP estimates long-run returns; the house edge is the casino’s average share. At 96% RTP, the house edge is 4%. Volatility affects how swings feel. In a short session, results can differ sharply from those averages.