Zorin will be down for a few days, well partially. It won’t be fully operational again for several days. Because Zorin 15 is based upon Ubuntu 16.04, there is NO support for bpfilters, and the currently Linux kernel has deprecated the old iptables filtering scheme so fail2ban and other firewall features do not work.
Because even though Zorin is a complete rip-off of Ubuntu, if one performs a do-release-upgrade it only updates parts and you end up with a Mix of Ubuntu 16.04 and 20.04 that does not play well together.
Thus the ONLY way to upgrade Zorin to Zorin 16, which is STILL based on a 2-1/2 year old Ubuntu, 20.04, is a fresh install which means re-installing all the applications and re-configuring everything which is several days work. I paid for the “Pro” version of the previous release under the promise by Zorin developers that they were working on an in-place upgrade but a year and a half later it is still vaporware so I am only installing Zorin core this time around.