Cocoa widgetset code is macOS 10.6 compatible.
However, when compiling on a newer macOS, it might be necessary to specify compatibility framework during linking the project.
By default, the linker uses the "current" macOS system.
Meaning a project compiled on a certain macOS version will run on the version, and likely will run on future versions.
Yet, it's not guaranteed to run on previous macOS versions.