Only partial client side caching in browser?

the performance of my nextcloud installation is slow. It seems, that there are only a few files getting cached by firefox. The most files are re-read with each request.
It is the same with each reqeust.

Even the logo.svg which is requested two times (?) - is only cached by the second request.

I am using Firefox, Debian 11 with php 8.1, MariaDB, Apache 2 with http/2 enabled. But i do not understand, why in most cases there is no client side caching (see screenshot)

Any hint where to look - what could i do wrong?

Thanks in advance