Port forward router troubleshoot

Hello, all!

I'm trying to run a Minecraft server on my system at home, and it SHOULD be a super simple operation. I have a port forward going to my system through the router (Netgear WNDR3700). Windows Firewall is disabled.

Port forwarding in general is working, e.g. my VPN connection to that machine works.

The MC server is running fine, because I can connect to it both via localhost and via LAN IP.

My ISP is not blocking incoming ports or connections.

Tried following these guides:        

https://www.purevpn.com/port-forwarding/minecraft

https://surfshark.com/blog/vpn-port-forwarding

When I try to connect, nothing happens, it times out, presumably because it can’t get through at all. So the question becomes: is there an easy way just to debug/isolate whether port forwarding is working in a router? The various Web based systems are too vague when it comes to trying to figure out if they work.

Thank you!