RTP is a long-run average; the house edge is the casino’s mathematical share:...

https://varimail.com/articles/does-session-timing-matter-in-online-casinos/

RTP is a long-run average; the house edge is the casino’s mathematical share: 96% RTP = 4% house edge. Volatility shapes how wins and losses arrive. In a short session, results can differ sharply from the average—RTP is no promise of a return.