I’ve narrowed this down a bit more. In macOS 13 and earlier, when adding an accessory view in prepareSavePanel, you never needed to do anything else on the document subclass. - (BOOL)shouldRunSavePanelWithAccessoryView would return true I guess automatically. In macOS 13.1b2, you need to implement shouldRunSavePanelWithAccessoryView and return NO for the previous behavior to occur. I can update my currently shipping app to do this, but I can’t update the previous versions. So it’s still a pretty big change IMO. Sample project is now attached to the FB.

Got the same thing happening with a 2015 iMac + an external Apple display.