Default project settings are ignored for new projects.
I just noticed this, but have no idea how long it's been going on. Current build of Kdenlive is from master git, updated on 2021-05-28
The options in particular that are being ignored from the default project setup is whether or not to separate channels, and the encoding profile for preview.
There may be other fields. The easiest way to test this would be to make changes to the default profile in kdenlive's settings, and then start a new project, and see if the default options have been applied.
Thanks for some great software!