Thank you for posting this too! I thought it was just me as well! =)
However, I have friends on iOS 16.2 and can backup WhatsApp.
I tried contacting WhatsApp via email since Christmas. They just told me that it will be escalated to their technical team.
So I think it could be a combination of both - iOS 16.2 and iPhone 14.
Am trying to get in touch with Apple Support again. I spoke to Apple Support in the morning, got a follow up call in the evening and they wanted me to go back to the initial Apple Support, much to my disappointment. I did ask for a replacement set but the technical team was reluctant. It was escalated to second tier of the technical team and the line got disconnected before we could resolve it. =(
Basically I have done everything possible - uninstall and reinstall WhatsApp, reset the network settings, try another Wi-Fi network, soft reset the phone, hard reset the phone and erase all data (twice) & reinstalled WhatsApp separately. All failed. iCloud backup is working but no one could answer me why I can't manually initiate a backup via WhatsApp. One technician told me that she never knew (for the last 3 years) that one could initiate a backup via WhatsApp. I rely heavily on WhatsApp for business. I sure hope WhatsApp or Apple can advise.