Which kdenlive packages are you using? If you are using them from your distribution, they might miss some important dependencies.

please inform which distribution and how you built/obtained the package... otherwise we can't help.

Check that a ffmpeg version is installed that actually supports mp4 containers and the necessary codecs. Thank you for your cooperation.

This is a last call to DAVE. If we don't see any useful answer within 7 days, we'll retire this report as INVALID. Thank you very much for your cooperation.

I have the issue solved now, Thanks.

I went into render settings and set it to render video also.

I do think an update caused this issue, as it always worked great before that update

Thanks for the update; closing.