RTP describes the long-run average return; the house edge is the casino’s...

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

RTP describes the long-run average return; the house edge is the casino’s expected share. A 96% RTP means a 4% house edge. Volatility affects how wins and losses are spaced—short sessions can swing sharply, so results may differ a lot from the average.