I’d guess its because you are using FTP passive mode and when you connect externally the port it picks is still blocked. Some good info on Active vs Passive mode here:
Since you can connect via the TrueNAS local IP just fine it would indicate that the issue is on router / firewall externally. You may want to review your router logs and details to see where packets are getting blocked.
FYI - Opening that wide range of ports is rather scary, don’t forward everything to TrueNAS like that
I have not ever used RouterOS as a firewall. However, I’ve used many different corporate, prosumer and consumer firewalls. In most non-consumer routers, just allowing ports through the firewall isn’t the same thing as a “port forward”, and is infact, only half of the equation. Your issue may be how you have your NAT rules setup. In this case, it sounds like a DNAT problem. Please see: NAT - RouterOS - MikroTik Documentation