Detecting the actual system font on OSX

You mean this report <https://xojo.com/issue/11322> which was for Carbon only ?
It may very well still apply for Carbon apps but we don’t ship a Carbon framework in current versions.
For older systems you might use the older Font Manager routines directly since you know they’re running on systems with Carbon API’s
Basically what Xojo presents is the Font Family name - not the specific variations (Ie/ Lucida Grande Bold Italic)
Carbon definitely made that more invisible that Cocoa does and would synthesize variations on the fly if the font did not have them
Unfortunately Cocoa doesn’t