Re-implement “1click transition“ or similar for video- and audio-transition.
Depends where do you do a right click to insert a “composite and transform” it will be added below that item. It should be possible between video tracks only. The option “mixed Audio tracks” has to be reconsidered or changed to “hide Audio clips”. See attached screen grab. Add_Transition
see https://bugs.kde.org/show_bug.cgi?id=404680 as well.