RTP is a long-run average; the house edge is the casino’s expected share: 96%...

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

RTP is a long-run average; the house edge is the casino’s expected share: 96% RTP = 4% house edge. Volatility describes how uneven wins can be. In a short session, results can swing sharply, so you may lose more—or win more—than the averages suggest.