When you say you are running Mojave, I think you probably meant to write 10.14.6 (not 10.16.6).

You could check you have the latest version of XQuartz (2.8.5) installed from,

https://www.xquartz.org/

You may need to reboot the machine after installing Xquartz.

Once back up, open a new terminal window and run the bash shell,

$ bash

Try putting your license file, e.g., license.txt. in your $HOME directory, and then set the environment variable FS_LICENSE to its absolute path, e.g.

$ cd $HOME

$ head -1 license.txt

me@somewhere.org.  <—— email address you used to register with

$ export FS_LICENSE=$HOME/license.txt

$ head -1 $FS_LICENSE