You can also run it on your Linux box and check external IP via web page. Sites like https://myip.wtf/text provide it in plain text that can easily be used without accessing your router’s UI.

Instead of connecting via your external IP, consider setting up DDNS (Dynamic DNS). Most routers support it out of the box, it’s free (using a DDNS service like DuckDNS) and easy to set up. Once working you’ll connect via a static URL rather than an IP and when your external IP address changes, that URL will update automatically within a few minutes and direct you to the new IP.