in order to see other servers you need to be on the same network as the host, if you are on the same Wi-Fi, you'll see their server. if you are on separate networks you can use a vpn to act like you're on the same network. if you're a bit more tech savvy you can forward port 1777 (i think this is the default port used by unreal) and your server will be discoverable by anyone else, i would suggest using a vpn however there are plenty of free ones that do just hosting a network online. i hope this helps, do let me know if you need any assistance!