When will the Sweet Bonanza bonus round come?
6x5 is the grid Sweet Bonanza plays on, and nothing on that grid tells you when the bonus round will come. How often the free spins start is not known in advance. One session can finish above or below where it started, whatever the RTP. Every spin is random, so a good run earlier in the session says nothing certain about the spins that follow.
Two RTP versions of Sweet Bonanza exist, and the one a player meets depends on the version run on this site. That choice appears only in the game rules. Read the rules before a session to see which return applies. The number tells you the long-run average, not what one visit will return.
21,100 times the stake is the largest win Sweet Bonanza can pay, and it is a ceiling reached very rarely. The multiple stays the same at every bet, so a bigger stake raises the money at that ceiling. No figure in advance tells you when, or whether, a session gets near it.