What happened to the rescale effect on Kdenlive?
What do you mean? Similar to the size parameter in the Transform effect? Or the ability to render the video at a different scale/dimension?
When I install Kdenlive with the previous version 23.04.1 before (I still have the version 23.04.2), it got removed from the effect list permanently.
I just checked 23.04.1 (appimage) and the effect is not there either. Can you provide a screenshot with the effect?
EDIT: It is there in 22.12.2. I suggest you log a bug report in bugs.kde.org
