Question Port forwarding and port 25565 issues

I can't take it anymore.
I'm trying to make a Minecraft server on my friends computer and even after port forwarding correctly and allowing connections through my friends firewall, it still won't let me connect.
He can log onto the server just fine using his IPv4 address that you can find after doing "ipconfig" in a windows terminal or by using localhost, but nobody else can. I've let all connections on port 25565 through on his fire wall (both inbound and outbound) and I port forwarded his IPv4 address correctly on his router config page. However, I am still not able to connect to his server using either his IPv4 address or his public ip that you can find by googling "what's my ip?" Also when I use websites like portchecker.co, it says that the port 25565 is closed even after port forwarding correctly.

What do I do?
To reiterate:
Port 25565 is allowed through the firewall
I port forwarded correctly (I checked all the websites and the videos and they all say yes)
Friend who is running the server can connect just fine through his IPv4 address
Port 25565 is still not open (connection timed out) when checked through websites like portchecker.co but the port is still listening.
Friend has both WIFI and ethernet, but is connected to the ethernet and is using the ipv4 address under the ethernet
server-ip in the server.properties folder of the server is left blank
The server is a paper server, but is not running any mods
I've followed ALL THE DAMN STEPS and have gone nowhere.
Any help is greatly appreciated.