Depending on how OS-independent it is, it might just be a matter of opening the project file and selecting Run -> Build (yes, the fact that Build is under Run is something that always bothered me, but it has been like that for 22+ years now). However the resulting app will be very "win-like" and when i was making macOS builds using Lazarus back when i cared about macOS i always had a "Macize" function i called at startup (ifdef'd for mac builds) that did things like replace the Ctrl modifier shortcuts with Command in menus (you can enumerate the menus, no need to do that by hand), move the About command to the apple menu, etc. There are also some other things that you may feel like doing.
TBH one thing that i wish was possible with Lazarus (at the time, now i don't care much :-P) was to be able to define different "layouts" per widgetset in a way that allowed you to use, say, a 'default' layout for Windows and Linux but a modified layout for macOS. Technically it is possible to design a form and then have another form inherit from it and apply modifications there, but it feels kinda awkward to use for different layouts (it is mainly meant for creating forms that you want to reuse but still have modifications - and it can be clunky in how it decides when to ignore changes in the base form or not - i do not use visual form inheritance, but i do use frames to design reusable controls visually and i often have to edit the source code of form files that use frames to remove overrides after saving the form so that changes to the frame are reflected in all forms that use it - this makes me want to add a readonly property to frames at some point :-P).
Depending on how OS-independent it is, it might just be a matter of opening the project file and selecting Run -> Build (yes, the fact that Build is under Run is something that always bothered me, but it has been like that for 22+ years now). However the resulting app will be very "win-like" and when i was making macOS builds using Lazarus back when i cared about macOS i always had a "Macize" function i called at startup (ifdef'd for mac builds) that did things like replace the Ctrl modifier shortcuts with Command in menus (you can enumerate the menus, no need to do that by hand), move the About command to the apple menu, etc. There are also some other things that you may feel like doing.
TBH one thing that i wish was possible with Lazarus (at the time, now i don't care much :-P) was to be able to define different "layouts" per widgetset in a way that allowed you to use, say, a 'default' layout for Windows and Linux but a modified layout for macOS. Technically it is possible to design a form and then have another form inherit from it and apply modifications there, but it feels kinda awkward to use for different layouts (it is mainly meant for creating forms that you want to reuse but still have modifications - and it can be clunky in how it decides when to ignore changes in the base form or not - i do not use visual form inheritance, but i do use frames to design reusable controls visually and i often have to edit the source code of form files that use frames to remove overrides after saving the form so that changes to the frame are reflected in all forms that use it - this makes me want to add a readonly property to frames at some point :-P).