I have recently started using kdenlive on fedora (linux) and it has given great results until my most recent project has given a bad quality result.

I have fiddled with the settings in both the render and project sections, but neither seems to affect it much.

Yes I am aware this has been asked before, however their solutions do not work.

If you need images, I have some, I just don't know how to provide them.

if you have squared/pixelated output using this rendering settings there is probably some issue with your project ... (started from a low quality image?)

make sure when you starting a project to import as a first clip the one that have your output resolution (for example 1920x1080) and accept Kdenlive suggestion to change project resolution to 1920x1080 (for example) .. and not a 640x480 or similar.

if the issue persist try to delete the Kdenliverc configuration file... and also use the "RESET CONFIGURATION" on "HELP" menu.

Thank you for the advice, but what if you have two clips of different resolution?

Kdenlive ask for a project resolution change ONLY for the first clip loaded.