SUMMARY STEPS TO REPRODUCE 1. Add some effects to clip 2. Create custom effect via "Save Effect Stack" menu item 3. Try to drag and drop this new custom effect to clip in project bin. OBSERVED RESULT Got an error: "Cannot add effect to clip" EXPECTED RESULT Saved effect stack successfully applied to clip in project bin. ADDITIONAL INFORMATION New custom effect can be applied to clip in timeline but not on clip in project bin. Video with this bug: https://youtu.be/98H8so2lcts
Custom effects are still not re-implemented: https://invent.kde.org/multimedia/kdenlive/-/issues/188
Thanks for you report, will close it here since we are tracking this issue at gitlab. https://invent.kde.org/multimedia/kdenlive/-/issues/188