I had the same problem with Splunk Enterprise 7.2.3 Build:06d57c595b80 (you can find this by going to Help > About on the menu at the top of your browser window when you've successfully got Splunk running on your host).
I needed to kill the splunk app that was running in the dock using Activity
Monitor, then run it again.
It then got stuck on another screen and I had to repeat that process
each time I managed to get one step / one dialog farther, until finally a browser window open to the the http://localhost:8000/ and the login fields appeared which I used to enter the username/password combo I choose/entered during the installation.
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