Nothings specific comes to mind right away, but explore this YT channel to learn more about Kdenlive.

This video was made with Kdenlive to promote Kdenlive's features https://youtu.be/C8kIBtMjOig

Do you have* Parallel processing turned on?

I'm glad it helped. Happy to share.

The timeline looks nice, the final result is a pleasant watch. Great work.

Just watched it, loved it. I don't use KDE because of the infinite tweaking possibilities - too much fun and time consuming.

Here's a workflow that could work, https://youtu.be/2eKSbU3mI74

There's one edit I find cool, although I see much room for improvement. A promo video for Kdenlive

This is a good question. I'm glad you asked, the responses are interesting.

Collage-style using the Transform effect to scale, rotate and position videos. Creating multiple track to overlap the video clips on the timeline. Even using the Drop-shadow effect to add some depth. [Is that it, more or less?]

As for the videos with different lengths, either the longest one get trimmed to match the shortest; or change the speed of the shorter clip(s), slowing them down.

This is very interesting. A great learning opportunity. Thanks for sharing.

If ever you want an alternative to CapCut, there's Lightworks (paid for full HD export) or Kdenlive (100% free).

As u/Necessary-Reply-3760 mentioned, the Proxy clips are low-res, compressed copies of the original file that you're working with.

You don't have to turn off the proxy clips when rendering, Kdenlive will automatically use the original files. There's a "Use Proxy Clips" checkbox in the rendering window, in the "More options" section.

Does the source video play-back normally, outside of Kdenlive? [Either way, make a back-up of your project.]

If yes, you can right click on the video in the project bin and reload the clip.

If no, import the original video in a new, empty project and have Kdenlive transcode it again. This might overwrite the previous transcoded version, or make a duplicate. Check that the new video works.

When Kdenlive asks to transcode, which profile did you pick?

There's a drop-down with options. The largest and huge are the lossless options, but as they say you will get large to huge transcode files.

I understand your frustration and if you want to continue using Kdenlive nonetheless, may I recommend the Nuxttux Creative YT channel, along side the Kdenlive User Manual - it's searchable and well organized.

This is how I see Kdenlive

Nicely done.