Plugin Admin: Multiple Filters number selector not displaying

Hi, in the “Viewing Records in the Plugin Admin” and in particular in the “Multiple Filters” chapter in the tutorial it says that “At the top of the list filter section is a selector the set the number of filter fields to use”, and just above there’s also a screenshot of how it looks, but that field simply doesn’t appear in my Admin page, I’ve looked for any other possible setting where I’m supposed to activate that multiple filters function, but can’t figure out where or how to do it otherwise.
Would be great if you could suggest a solution, many thanks!

https://ww.wp.xz.cn/plugins/participants-database/