Am I right in thinking you posted elsewhere that you are running the Flatpak version of KDEnlive? The issue with flatpaks (and snaps) is they run separate to the system. I only use Synaptic Package Manager which installs the APT version and have no issues rendering and uploading to my Vimeo account. I have removed gnome-software. And I only login to Zorin on xorg (X11), never Wayland.
Latest video using KDEnlive on Zorin 17.3 Core bare metal install:
