Thank you for all your comments. Checking your answers and doing some work I’ve been able to install Lazarus in my new computer.
This is no the first time I've install Lazarus in Mac OS X. I always used the installation programs available in the Lazarus main page (
https://www.lazarus-ide.org), which sent me to the sourceforge project
https://sourceforge.net/projects/lazarus/files/. What I can said is that in my system: A new mac-mini with Mojave up to date (10.14.5) and Xcode (10.2.1) the installation of the fpc available in Sourceforge for Lazarus does not work, because it does not detect Xcode.
Also, In general I followed the suggested order: first fpc, then fpc-source and Lazarus finally.
Until now I didn’t have problems in Mac OS X.
Anyway, I found different alternatives. One was with Homebrew. I tested the installation of fpc with this tool, as the fpc available in homebrew is exactly the same that is in the main page of Lazarus, and it worked. The fpc-src and Lazarus were installed the normal way, (not using brew) and Lazarus recognized the correct paths of the compiler and debbuger.
Also I visited the Freepascal homepage (
https://www.freepascal.org) and I went to the sourceforge mirror for Intel/i386 (
https://sourceforge.net/projects/freepascal/files/Mac%20OS%20X/3.0.4/) and I downloaded the fpc-3.04a.intel-macosx.dmg package which also I was able to install without problems.
So for my new Mac OS X system, the installer available in sourceforge from Lazarus does not recognize that xcode is already installed, but that from Freepascal works well.
Another anecdote was that once Lazarus and fpc were installed, I was not able to compile the most simple application (an empty GUI Form) as I got an error message from CarbonBars about only cpu i386 is supported, but this time I knew how to fix this problem, in the menu Project > Project Options I selected Config and Target, to select Darwin as the Target OS and x86_64 for the Target CPU family and also I changed the LCL widgetset, which is carbon by default, to cocoa.
I think these instructions may be important for a beginner trying to install Lazarus in one of these new Mac computers with Mojave.
Thank you