It would be much better if you could post the log. However, am I reading correctly that you are just trying to start the Appium server with ‘–app’? Don’t you at least need ‘–deviceName’?
For the 'depreciated error, I think Appium may want you to give the parameter like this:
Re-reviewing this, I think my real issue is that ever since Appium.app stopped being maintained I migrated to Appium server CLI. I’ve attempted to follow the directions here: https://medium.com/@SimonKaz/dealing-with-outdated-appium-gui-server-version-3cb2be8a9fcc#.yr7gl9jfr for configuring Appium.app to work with the CLI but for whatever reason it fails to launch the server, thus cannot use the Inspector.