"docker: failed to register layer" on Proxmox

Stop the running LXC container.

Append lxc.apparmor.profile: unconfined to the Apparmor settings for the specific LXC container (example: 100).

Example

/etc/pve/lxc/100.conf

arch: amd64
cores: 1
hostname: example
memory: 1024
nameserver: 192.168.0.2
ostype: debian
rootfs: local-lvm:vm-100-disk-0,size=12G
swap: 1024
lxc.apparmor.profile: unconfined