I'm running kdenlive 22.04.3 on ubuntu 22.04

I have a clip that I want to insert into a track.

The timeline has two video tracks and two audio tracks.
That suits me, because I want to have a cover that fades out after a few seconds.
So I have the cover in the top track.

I then attempt to drag my clip from the bin to the second video track.
The clip can be dragged into the top drag, after my cover.
But it refuses to drop into the second track.

This doesn't suit my project at all: I need to edit clips that overlap each other.
Because the GUI shows multiple tracks, I assume that this is possible. But for some reason kdenlive seems to insist that I only use one track.

Do you just want to have 2 clips, one in the first track and one in the second track?

Adding the second track is not possible if it has both audio and video and the second track is audio-only or video-only. From your first post I understand that you have 2 tracks, both AV (audio+video) so it should work fine.
Try to delete the unused track and add a new AV track to the project.

Also check that the second track is free. If you have another clip on it and the space is not enough to insert the new track, it won't work