FaceTime audio discrepancy in China variant Apple devices

I am using 4 apple devices, one is iphone 14 pro max(singapore), iphone 12 mini(USA) both of them have facetime audio. The problem starts with my iphone 12(china variant) which doesn’t support facetime audio, i get that, china doesn’t allow you to use facetime audio option in their apple devices, but the weird part started with my 4th device which is ipad 9th generation (china variant) supports FaceTime audio call. I don’t understand how is that possible and why it is not possible on my iphone 12(china variant)? does anyone have any answer for it?

[Re-Titled by Moderator]