If you compile an AppKit app with the macOS 14 SDK in Xcode 15, the default font size of several NSControl subclasses increases from 12 to 13 when the app runs on macOS 14 Sonoma. I discovered this the hard way yesterday when I noticed that my box—an NSBox, that is—was no longer big enough for my controls.
I haven't done an exhaustive review of NSControl subclasses, but I've confirmed that the change affects NSButtonTypeMomentaryLight, NSButtonTypeRadio, NSButtonTypeSwitch, and NSTextField. Unaffected is NSPopUpButton, which already had and continues to have a font size of 13.
I should offer the qualification that my testing was done with controls created programmatically. I'm not sure what happens to controls inside nibs/xibs/storyboards, since I'm (in)famous for working without a nib.
The font size increase on Sonoma is somewhat baffling and also completely undocumented as far as I know. There's not a peep about it in the AppKit Release Notes for macOS 14, the macOS Sonoma 14 Release Notes, or the What’s new in AppKit video from WWDC 2023.
Needless to say, I won't be filing a Feedback…