It opens normal. When try to click "Open" (beside "New" and "Save" it freezes. All I can do is close it via System Monitor. Happens every time and makes it kinda unusable.
You'll need to provide more details. I last tried to reproduce this on a clean budgie, and the dialogs opened without issue (and appear to be gtk dialogs).
What desktop and theme are you using?
Does QT_LOGGING_RULES="*.debug=true" kdenlive suggest anything interesting (or strace kdenlive)
So I opened it via "QT_LOGGING_RULES="*.debug=true" kdenlive" and it works. Now it also works if I open it normal. I really don't know why it works today. I tried it some weeks ago and also yesterday (even uninstalled and reinstalled several times) and it always froze. I guess we can close this. Thanks for the help!