I think the problem with Clear OS is that it has a very narrow market. People comfortable with Linux and containers have their own preferred method. And band new users don't know it exists.
As for your OPNsense issue, I have never seen anything like that before and can not understand it. Hardware conflict perhaps? You can also try OpenWRT or there is a free Sophos firewall. Also Firewalla, but it is a bit old...
When you turn your NAS into a hosting platform, it is no longer just a NAS.