Let me preface by saying I've made more private servers than I can count. I'm on a 2017 Macbook Pro running catalina, the server is showing up as fully functional and I haven't changed any of the settings at all. I have centurylink fiber connection and I have pretty decent upload/download speeds. The router is a Calix C844G. I've port forwarded on TCP/UDP and I've also added a custom service to the firewall in the router config. Even now I can't connect to the server whether I'm on the computer the server is running on on the same network or on another computer not connected to the network. I'm at a total loss and I've literally never run into this before. Usually with the same symptoms I've made a mistake with the port forwarding or my ipv4 address changed because of a reboot or whatever but everything seems right? Also I have my computers firewall turned off and that doesn't seem to affect it at all.
EDIT: I tried just disabling the firewall in the router config and it didn't have any effect (also added router info)
Well, first step is to be able to connect to it locally. If you can't do that, then trying to figure out the firewall and such is wasted effort. When the server is up, if you open terminal and do lsof -i -n -P|grep 25565 does that show anything?