https://wiki.freepascal.org/Installing_Lazarus_on_MacOS_X

Carbon and Cocoa
At present (early 2019) Lazarus using Cocoa will meet many users needs. Carbon work pretty much as expected but you are advised to try Cocoa first, especially considering that Apple has indicated releases after Mojave will not support 32bit Carbon. Alternatives include QT and GTK2+, both requiring additional libraries and GTK2+ on the Mac appears to get little attention these days. QT on the Mac does have some strong supporters on the forum.

However, we should assume, Cocoa is the future on Mac. It is possible to build an all Cocoa version of Lazarus with release 2.0.0 and later. It is also possible to make a Carbon install of Lazarus and use that to generate Cocoa 64bit binaries. In a Carbon IDE, you need to set the Target to the 64bit processor and select the Cocoa Widget set:

Open your project with Lazarus and click Project/ProjectOptions
In the "Config and Target" panel set the "Target CPU family" to be "x86_64"
In the "Additions and Overrides" panel click on "Set LCLWidgetType" pulldown and set the value to "Cocoa"
In the past, for some reason Lazarus kept setting the compiler to "/usr/local/bin/ppc386" - which results in 32 bit apps. Make sure under Tools->Options that "Compiler Executable" is set to "/usr/local/bin/fpc" to get 64 bit apps.
Now compile your project - and please feed back any problems you experience.

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