The below should provide the splits you desire. The bookmarks designate the last page of a segment via "bookmark end interval" and "divide into fixed bookmark delineated jobs"/"1 bookmark per job" designates that each split segment will be a separate subjob.
I read about the feature in patch notes, upgraded FF Core to the latest version, but now looking at the options of Split node, I don't understand how its supposed to be used with bookmarks at all.
For example - a file with 100 pages which is supposed to be split into 40, 40, 20 pages, in total 3 jobs, with bookmarks placed on pages 40 and 80 to indicate where the split is.
What settings should be used in this case?