I too have struggled over the months with OSX compiling. I found the compiler path hint above via a discreet line in one of the wiki pages (the page I now cannot find again...I can't remember how I found it in the first place but this is my point : it is not mentioned sufficiently enough, though I see it mentioned more in this forum now so word is spreading) some months ago but its such a subtle mention for something so significant. With OSX Catalina now in beta and out soon, all applications have to be 64-bit yet Lazarus is still configured for default 32-bit use on OSX.
I've spent a while with trying the Cocoa widget set, as Carbon is still the default which is a 32-bit widgetset. I found that building an application for Cocoa via the Project Options on my 64-bit Mac often caused conflicts with some of the packages, displaying compiler errors relating to 32-bit. So until recently I could only make a 32-bit version for my users, for OSX. Eventually, only by rebuilding the entire Lazarus IDE to use Cocoa (via the Configure Lazarus settings), setting the compiler path /usr/bin/fpc etc could I get these packages, and therefore my application, to cleanly compile as a 64-bit application which I am delighted about, but it hasn't been straight forward like it is on Windows.
It's wonderful that Lazarus allows such cross-platform development. For OSX systems, it would be great if we could get it a bit more stable out of the box, so to speak. Maybe its time to make the OSX version of Lazarus Cocoa by default, and the default compiler path in global settings set to /usr/bin/fpc? This would surely help of people new to Lazarus who want to try it out for OSX development.