SUMMARY
Today one can define default folders for the project, temp files, capture, library and - for whatever reason together - rendering, titles and scripts. Kdenlive creates a cache folder for every project in the default project folder using a seemingly random number as the folder name.
I suggest two options: 1) The user can specify where kdenlive stores cache data; 2) kdenlive creates a (hidden) .Cache folder in the default project folder and creates the individual cache folders there (that way they are out of the way)

While we are at it, I motion to separate the default folder setting for rendering, titles and scripts. They have very little in common, and I would like renders to go to a different folder than scripts or titles. Titles, for example should be in a sub-folder of the project folder (potentially to be specified in the Settings).

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Pop!_OS 22.04
(available in About System)
KDE Plasma Version: 
KDE Frameworks Version: 5.101.0
Qt Version: 5.15.7