Forgotten gives no promise on any single spin
Every spin lands a fresh set of symbols, and three or more Book symbols anywhere on the grid can start the Free Spins round. When that happens is not known in advance. How often the bonus round comes cannot be predicted, and the result of one session is random whatever the RTP.
Each spin runs on one of the listed RTP versions, and which version this site runs is shown only in the game rules. The version sets the long-run return, so the rules are the place to check it before the first spin.
Symbols on the grid can add up to the maximum win of x7,500 of the bet, a ceiling that is reached very rarely. The figure is a multiple of the stake, so the money amount depends on the bet you choose, and no spin is promised to reach it.