Drawing over the video

First, configure Kdenlive to use Gimp as default image editor.

Go to Settings > Configure Kdenlive > Environment > Default apps > Image editing: gimp-2.10

Over the video preview, right-click > Extract frame to project > over the project assets, right-click over the image > Edit clip

At Gimp, create a new layer (via top menu), draw some stuff, then delete the background layer. Then overwrite the file. Go back to Kdenlive.

Drag and drop the edited image into video timeline.