SUMMARY When using the mix clips/same track transition, kdenlive will display an error if there is not sufficient frames outside the timeline clips. I suggest that kdenlive in that case displays a dialog saying "Not enough frames at clip end to add transition. Adjust automatically?", with a "don't ask again" checkbox and yes/no buttons. If the user selects yes, go ahead and adjust the clips as required. After all, this is likely what the user wanted ;)
With version 24.08.2 mix adjustment according needed frames is automatically done by Kdenlive. I closed this bug. If it still appears in the latest version, please feel free to re-open it and update the affected version number.
As far as I can tell, this is not fixed. I just installed 24.08.2 and dragged 2 video clips side-by-side on a video track. I double click the edge of one and get "not enough frames at clip and to apply the mix". I have to manually resize the clip to be smaller for it to work, but I agree with Anders; kdenlive should do this automatically, resizing the clip just the amount needed (or perhaps resizing both clips either side 50/50) for the mix to be applied.