RTP is a game’s theoretical average return over a very large number of plays,...

https://josuesexpertblog.novacrestiq.com/posts/why-do-two-slots-with-the-same-rtp-feel-totally-different

RTP is a game’s theoretical average return over a very large number of plays, while the house edge is the share the game is expected to keep. For example, 96% RTP = 4% house edge