cache does not empty completely

Hi, What settings do I need to change to completely clear the cache? I've tried everything I know, but I still have the problem that cookie settings, for example, can't be changed afterwards because they're stuck somewhere in the cache. When I open a new private window, the cache is completely empty. Why can't I do this with an existing window? By the way, I have: Firefox Developer - 143.0b2 (64-bit) on the aurora update channel.

Thanks, Dietmar