Today: Kdenlive uses a very convenient two monitor concept. The clip monitor is, you guessed it, for working with clips. In contrast, the project monitor shows what the final outcome of your clips+transitions chaos in the timeline will be: this is what will be rendered. Now, both monitors come with a «split view». So I would expect this to be the same functionality?
Well, both «split views» are actually completely different things. In the clip monitor, «split mode» splits the clip display into two halfs, one part showing the clip before effects are applied to the clip shown, and the other part shows the final result of applying all effects. In contrast, the project monitor in «split mode» instead shows four quadrants (instead of two halves). Each quadrant then parades one of first four tracks that are currently visible (unhidden).
Thankfully, when made aware of the misnaming, the Kdenlive developers kindly renamed the multi-track split view mode of the project monitor into, well, «multitrack view». In the future, this should hopefully avoid further confusion ... and not only on my side. Small UI changes, yet very important for an overall smooth Kdenlive experience to both newcomers as well as seasoned hands.