If you see an error message in FileMaker Server installer like this, you may need to remove or disable the built-in web server software to be able to install FileMaker Server.
So in order to disable it, you can dig into how to disable services in MacOS. But we found a simpler way. Just move the com.apple.serverd.plist out of the /Library/LaunchDaemons folder and restart the Mac.
We'd prefer to change the ports from either MacOS Server's web server or the FileMaker Server's web server, but both is not supported. As you may guess a lot of code simply expects https at port 443, so they don't even bother to offer you a way to enter a port number.