I am on VE8.2.7.
If using ubuntu-24.04-standard_24.04-2_amd64.tar.zst for LCX or after upgrading to 24.04 the LXC is not working anymore for me, as well.
Adding "lxc.apparmor.profile = unconfined" to the LCX config solved this.
Confirming nesting=1 fixes this. It also doesn't look like the manual change to disable apparmor was persisting for me. I'm new to proxmox so may be user error. This one was driving me a bit crazy so thank you all for solving it here!