This document will guide you on possibly fixing the FaceTime features when using a macOS virtual machine.
The FaceTime features require macOS Monterey and newer
Keep in mind, the FaceTime features are experimental and may not always be 100% reliable.
Virtual machines typically do not have a microphone or webcam plugged into it, so when FaceTime tries to load and use the default audio/video devices, it fails and causes calls to fail.
A possibly way to fix the issue is to install "virtual" audio/video devices on your Mac so that FaceTime can use those.
Complete the following steps on your macOS virtual machine
Download & install a virtual audio device: https://vb-audio.com/Cable/
Download & install a virtual video device: https://obsproject.com/
Open OBS and Start the Virtual Camera
You only need to do this once to register it with the system and show in FaceTime
Reboot your Mac
Open FaceTime
Using the FaceTime status bar menu...
Select the OBS virtual camera as your video source
Select the VB Audio virtual audio device as your audio source
Now that you have virtual devices setup for both your audio/video inputs, FaceTime calling/answering should be more reliable.