The layout switcher that lets you switch between Logging, Editing, Audio, Effects and Color resides in the top right corner in the menu bar. But because I use a global menu in Plasma, the menu bar is not shown inside the kdenlive window, thus the layout indicator is nowhere to be found.
STEPS TO REPRODUCE
1. Add a global menu widget to your Panel in KDE Plasma
2. Open Kdenlive
The layout switcher is gone, as it is not shown in the global menu.
The layout switcher is still shown somewhere, even though there's no menu bar inside the kdenlive window.
I know that you can switch between layouts using keyboard shortcuts or the "View" menu, but that is not as convenient and most importantly there's no visual indication what layout you are currently in.
Thanks for your report! Yes, the layout switcher is part of the menu bar. This is also a problem on macOS (we are currently trying to bring Kdenlive to macOS). Hopefully we will find a solution soon.