Yep, looks like you are right. Had a look in Kdenlieve APP, didn't see an 8K setting for rendering, I would have assumed that they would have had support for 8K after the recent update but nope.
Its ok honestly, most people don't even upload their video's to Youtube in 4K let alone 8K. Most still upload in 1080P or less, which I think is kind of weird. Cause I have had a 4K action cam for years now, and I would upload in 4K most of them time.
Anyways, here is the features list for the latest Kdenlive...
https://kdenlive.org/en/features/
The APP is a lot different then it was, so I am going to have to re-learn it a bit before I start being successful with it again. But they brought back the RENDER button again which is great, never understood why they removed it in the first place.
For some reason in the previous update they removed the RED RENDER button, and forced us to have to go to PROJECT in the title bar, in order to click on RENDER, which all that did was add an extra unnecessary step. Glad they fixed that.