Hello, first of all thank you for the guide. If there is anyone who could not access the link for GUI, here is the solution:

docker run --name fethinifi -p 8443:8080 -e NIFI_WEB_HTTP_PORT=8080 -i -v C:\Users\fethitekyaygil\Desktop\:/opt/nifi/nifi-current/ls-target apache/nifi

The problem is 8080 is actually the HTTPS port, in the command above you are saying that you will use http port.