I’m glad it worked in the end.
The way Kdenlive handles clips with a video and an audio stream is something to get used to. Kdenlive sees a clip with video and audio but it has to separate them into a video track and an audio track. By default, V1 corresponds to A1, V2 to A2, and so on. If you create additional video tracks and plan to put clips in there that have an audio stream, you need to create a corresponding audio track.
I’m not sure why this happened because when you move a clip from one video track to another, the audio stream is moved to the corresponding audio track (V1/A1 → V2/A3). If there is none, the clip cannot be moved.
This behavior is the case for clips with video and audio streams that have not been un-grouped. You can select a clip, right-click and select Ungroup. After that action, you can move the video portion of the clip independently from the audio portion - they essentially become two separate clips in the timeline. Note that you cannot undo this later. The only way to group them is to select both clips, right-click and select Group Selected Clips.
If you just need the video or audio stream of a clip in the bin, you can drag the clip to the timeline using the video or audio icon that shows up when hovering the mouse over the clip in the bin. The same feature is available from the Clip Monitor.
This happened because you must have enabled the Timezone Insert Mode.
It is this little icon that tells Kdenlive to insert a clip into the area identified by the blue bar above the timeline. You may want to read
this section in the Kdenlive Manual.
That’s because the video and audio portion of the clip are still grouped as I have explained before. You need to ungroup them to be able to delete the audio stream of the clip.
In your scenario, it is better to just drag the video portion of the second clip to the timeline.
I know that Kdenlive can be intimidating at first, and its features and functions, menu structure, and the way it handles clips can be confusing. That’s particularly true for anyone venturing out into video editing. I suggest you browse the Kdenlive Manual and start with the Quick Start chapter.
If you are more of a visual learner, there are several good tutorials for beginners on YT (like this or this).
Have fun, and always come back here if you get stuck or need advice!