After doing a system update and starting kdenlive I got the a pop-up window with the message cannot find mlt profiles and a suggested path of /usr/share/mlt/profiles . After reinstalling melt and kdenlive and getting the latest versions etc I found out that I just should have looked for the correct path. On my system are two that I could use. /usr/share/mlt-4/profiles and /usr/share/mlt-5/profiles . Of course I chose the newer /usr/share/mlt-5/profiles . It took awhile for me to figure that out.
If you have 2 mlt versions installed it is best to uninstall kdenlive and both mlt versions and then reinstall kdenlive and let the system solve its dependencies so it will install the correct mlt version (mlt-5 in my case).