GL-AR750 Ports are closed, even though I opened them?


I have a GL-AR750. I connected my RaspberryPi to the router and tried forwarding the Port 25565, which is used for a Minecraft Server, but it doesnt seem like it worked and some port checkers also tell me that the port is closed. Can anyone help me? I spent hours looking for a fix, but I cant seem to fix it.

Is the AR750 directly connected to your ISP or is there another router in between? Is the IP you get from your ISP public or behint a carrier grade NAT?