Wifi calling is a bit of a misnomer; Wifi calling works on both WiFi and cellular data.
I use WiFi calling on my Iphone SE 2022 3rd generation which is a 2 line phone; 1 line is Telcel Amigo prepaid and the other is Tello a US carrier; no problems anywhere. I use Tello in Mexico to make and receive calls to Canada and the USA on WiFi with Totalplay and on cellular data with my Telcel Amigo prepaid plan. When travelling which I do quite a bit; my Tello line works with Wifi calling everywhere I go including Canada, Europe, Africa and last week in the Bahamas; on WiFi on cruise ships, hotel Wifi or a cellular connection with a data Esim. Works for both calling and receiving calls.
I have never tried using WiFi calling on my my Telcel line other than using the cellular data connection while in Mexico.
On a cruise ship you need to have the unlimited data package to receive calls; not the packages where you connect and then disconnect every time you use the internet.
In 3 years using Tello it has always worked; I think the important issue is the US carrier and getting the right settings on the phone.
Tello has many great packages; I pay $7 USD per month plus tax for 100 calling minutes, 2 gb data and unlimited texts.