We are using CallKit framework to benefit native usage for Voip features. Users can make Voice and Video Calls in our Messenger App.
But Apple removing CallKit apps
One thing you could try, even though it may not work: disable callkit functionality based on the locale region. This may be enough "proof" that Callkit is disabled for China from the legal perspective in order to be approved for the Appstore. Then your Chinese customers could just switch the region in the settings to get Callkit. This would be already "their" problem so to speak.
Disclaimer: I'm by no means a lawyer or anything, follow this advice at your own risk.