I’m not sure what is happening.
I installed PMS 1.29.1.6276 on my 2011 MacBook Pro (i5-2415M). It is running macOS 10.13.6 and has Safari 13.1.2.
It wasn’t the fastest, but the installation was straightforward. It proceeded normally and let me claim the server and get to server settings. This was using Safari.
macOS did flag Plex Media Server when I launched it the first time. I went to System Preferences → Security & Privacy, granted permission, and PMS launched OK.
I looked at Plex Media Server.log on my system. Other than the GET /:/prefs returning 200 instead of 500, there were no major differences.
There are problems using Safari on macOS 10.11 and 10.12 systems. The navigation bar in Plex Web is not available (thread). However, I’ve no idea if this would affect initial setup of PMS.
Wish I could be of more help.
