Camera Raw is used from Lightroom when one invokes the Edit in Photoshop command. For this to work, Photoshop and ACR must be on version parity. So if you had an older or newer version of PhotoShop or Lightroom Classic, LR will pop an error telling you it must render the image, not ACR. Is this what you're referring to?
Author “Color Management for Photographers" & "Photoshop CC Color Management/pluralsight"