SUMMARY
When rendering to any kind of format, the status job hangs on 'waiting'.  
Running it with 'snap run kdenlive' I get the following output from terminal:

* CREATED JOB WITH ARGS:  ("/snap/kdenlive/39/usr/bin/melt-7", "/tmp/kdenlive-HCXNSD.mlt", "/home/hiparco/Vídeos/sag.webm", "-pid:18898", "-out", "4876")
starting kdenlive_render process using:  "/snap/kdenlive/39/usr/bin/kdenlive_render"
Qt: Session management error: Could not open network socket
dbus[19266]: arguments to dbus_message_new_method_call() were incorrect, assertion "_dbus_check_is_valid_path (path)" failed in file ../../../dbus/dbus-message.c line 1366.
This is normally a bug in some application using the D-Bus library.

  D-Bus not built with -rdynamic so unable to print a backtrace


STEPS TO REPRODUCE
1. Open kdenlive;
2. Drag media file to track;
3. Start rendering to any file.

OBSERVED RESULT
Status job halt on 'waiting...'

EXPECTED RESULT
Start and finish the rendering process.

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: Kubuntu 20.04
(available in About System)
KDE Plasma Version: KDE 5.68.0 / Plasma 5.18.5
KDE Frameworks Version: 
Qt Version: 

ADDITIONAL INFORMATION