colorsync compatible merely tries to guess stuff, 1-2-1 is always incorrect 
stuff will always revert to beign tagged 1-1-1 once uploaded anywhere so its a inconsitent “hack” that should be avoided especially as newer macbooks in reference mode will show a over contrasty image when you feed it 1-2-1 this is really depreceated of a workaround for a problem that doesnt even exist.
Transfer function shouldnt be undefined, its rec709 , 1.961 is correct, if your display is 2.4 you get a total system gamma of 1.22 as per rec709 specs. thats how it should be and how any camera on esrth handles rec709
the issue is apple manages rec709 tagged content wrongly, it assumes a bright surround viewing environment and thus a ootf of 1 which is why people start to freak out, but on xdr displays you can now just put the ootf back into the inage stream on the display side and bobs your uncle (choose xdr rec709 preset)