Thanks for your help Stéphane!!
Yes, after starting a ubuntu container and enabling apparmor, that worked fine.
I looked through the config of the ubuntu container and compared it with the debian config and I realized that the main difference is that securityfs is by default mounted in the ubuntu container and in debian not.
I mounted securityfs in the debian container and apparmor started to work as expected.
lxc.mount.entry = /sys/kernel/security sys/kernel/security none bind,optional 0 0I still have a question though, I read here: https://wiki.ubuntu.com/LxcSecurity
and there it says that you should not mount securityfs in your container.
So how are you supposed to reason around this?
To be able to increase the security with apparmor, you have to lower the security a bit?
Many thanks!!