How can i set Permissions for Specific Users so they can only Write in theyr own Category (we host gameservers and the S-Admins from these shoud be able to write in theyr Server Category but not in the server category of others)
Permissions are for groups. You will need to create a group for each user.
there is nothing about special write/delete blabla permissions
You need to create a group and a category for each user that you want to have a private category. Understanding groups and category permissions