You don’t need a service like that in any way, you don’t have to use steam, epic or other, you can simply connect with IP addresses “Minecraft style”
You only need the services if you want to be able to send an invite or get a list of sessions, etc
Something like hamachi should have worked if multiplayer was setup correctly, as hamachi essentially puts you on the same LAN, you should be able to type in the IP provided and choose lan and it’ll find it
Image stolen from here