I searched something on the web and found that the /app/tmp directory could be missind. So I mkdir the directory and chown it to www-data but the problem is still present.
Hey garett, this wasnt the problem! I followed https://help.passbolt.com/hosting/install/ce/debian-10-buster.html and there was no line saying that I have to install some of the plugins especially for php manually. So i asked someone who has even setup an installation and he told me that dependencies are missing, there wasnt sth. wrong with the folder.
but thanks to you too! maybe the developers should have a look a their installation script which not works properly?