It looks like TPG SIMBA mobile is able to convince Google to provision VoLTE on Pixel 4 XL. It is not known if the VoLTE is enabled for other Pixel devices. e.g. Pixel 3a or Pixel 6 Pro. Do comment below if it’s working for you.
If SIMBA can do that, I am just wondering why is it that M1 provision VoLTE to work on Pixel devices.