Your first session and the bonus round
Symbols land on the 6x4 grid at random, so the bonus round can arrive on the first spin or after a long run of plain spins. How often that happens cannot be known in advance. The result of one session is also random, whatever the RTP version behind the game.
Each spin on the 6x4 grid follows one RTP version, and the version Ubet Casino runs is shown only in the game rules. The five versions sit close together, so the difference in return is small.
Winning symbols on the 6x4 grid can pay up to a fixed multiple of the bet, and that ceiling is reached very rarely. The maximum win works as a limit on the payout, not as an expectation for any session.