Currently the TYPO3 backend is slow in docker installations. Even if a delegated volume is mounted.
If TYPO3 is setup as composer we can stop mounting the /var/ folder to the docker container.
I ran some Tests after removing the folder from mounting to docker and it runs a lot faster, especially the backend.
There might also be reasons to remove the typo3temp folder from mounting inside the docker container, but currently I don't even know what or why TYPO3 stores still data inside that directory.