It is in fact not that secure by default. It lacks a way to manage the desktop in mass. Not to mention is also lacks a firewall and selinux but those can be enabled. Also I wouldn’t trust the lock screen as it can be bypassed because it is Xorg.
Linux Mint is very good for general usage but I doubt its security in a military application. It is better than before which is good.
Honestly China makes me really sad. It has such a long and rich history and now the government seems to be completely separated from the government.