My comparatively old Panasonic DMC-FZ200 (released 2012) has this in the manual for play mode:
[Face Rec Edit]
You can delete or change the information relating to Face Recognition for the selected picture.
1 Select [Face Rec Edit] on the [Playback] menu. (P52)
2 Press 3/4 to select [REPLACE] or [DELETE] and then press [MENU/
3 Press 2/1 to select the picture and then press [MENU/SET].
4 Press 2/1 to select the person and then press
5 (When [REPLACE] is selected) Press 3/4/2/1 to
• When all Face Recognition information in a picture has been canceled, the picture will not be
categorized using Face Recognition in [Category Selection] in [Filtering Play].
So it does recognise several faces (I think you can store about 10 faces it should recognize by name) and will prioritise them when doing face-based focusing. It will also label them on playback and allow selective playback of images containing them.
I haven't used this functionality so I don't know which form it is stored in: I would suspect some EXIF tags getting used rather than XMP (but of course this should be reasonably straightforward to convert). Since this sounds like the kind of feature earning a checkmark in camera tests and since it already was available in 2012, I should be surprised if it isn't buried somewhere in the menus of most current-day offerings in some more or less useful manner.