I get the error You are running VisualVM using Java Runtime Environment (JRE) when starting. However, on my disk there is a folder java-1.8.0-openjdk-1.8.0.392-1 and I added it to the PATH variable.

Could be the "default" java installation your OS is trying to use could be missing or incomplete? I'm afraid I'm not a mac user, so I'm kind of feeling my way around in the dark here. But on Windows, ...