I went to one a few years ago. It used to be that folks who won the $20 slot tournaments that used to be held on every cruise were invited to a big tournament every year. I think they also invited some of the "high rollers" too but I got in because I won one of the tournaments. For the big tourney, they assigned people times to play the first round. You beat the heck our of the buttons and the scores were recorded with the highest scores qualifying for the next round. I had a terrible machine and so after my three minutes I was done. That machine didn't do well for anyone and was very tight but it's all luck. I'm fairly certain that the top 5 won money, with the highest scorer winning $35,000.
Not sure if this is how they will do these but here's more verbiage from the email, and you can probably call to find out the rest of the details of your offer:
"What's better than the sound of a winning pull in our friendliest casino at sea? How about big plays and unforgettable moments. Anytime from fall 2022 to spring 2023, choose to join six slot tournaments with prizes totaling $25,000 each cruise or compete for a share of $100,000 on our grand prize tournament cruise — exploring the Panama Canal, the Caribbean and the Mexican Riviera as you play for a share of the $250,000 pot."