I just got off a long chat with Verizon and learned the following. Cutting and pasting what they told me.
This is a known issue. The alert states:
“Some customers with iPhone 12, iPhone 12 Mini, iPhone 12 Pro, or iPhone 12 Pro Max may be experiencing issues with making or receiving calls on Wi-Fi calling. Users may also experience drop calls with Wi-Fi calling.”
“Apple is currently working on this issue and will be releasing the fix in an upcoming software update, although we don't have an exact date as to when that update will be released. Some routers broadcast both a 5GHz and 2.4GHz signal. The 5GHz connection will be faster but have a shorter range. Have you tried connecting and using wi-fi calling with both of these signals from your router (if available)?”