Rendering on Flatpak or AppImage versions of Kdenlive is a lot slower than using the one from Fedora's repository. It seems like that Flatpak and AppImage are limited to 1 core. For example on Flatpak or AppImage my last project would take 1 hour and 40 minutes to render (<20% CPU usage). On the one from Fedora's repository it would take 22 minutes (>80% CPU usage). I'm using Fedora 39.
Same trouble, with a very slow rendering. 40min for 20min video. Few cores are used but at less than 30%.... With parallel rendering. AMD 5800X AMD 6950XT 32 GB ram I tested all versions arch, flatpak or appimage, all are impacted when kdenlive is 24.05. Tested also with debian.
Thank you for reporting. This is a known issue as Kdenlive has to render all effects by CPU. You can try rendering with GPU profile, nevertheless Kdenlive has to switch back to CPU for the effect rendering. GPU effects and GPU rendering is on the roadmap as mid term goal.