I see a lot of HIToolbox calls, which is what AppKit uses internally to draw. So from that third to last link, it seems like a hybrid solution. Not optimal but still better than Electron or Flutter.
> I see a lot of HIToolbox calls, which is what AppKit uses internally to draw.
sure, but that's not the same as using a NSComboBox directly, and that's not using Apple's layout engine (based on cassowary, wasn't it) either. Not that I think that this is a bad solution : it allows software with a strong identity to have fairly custom UIs that are consistent across platforms.
