Samsung Galaxy S20+ 5G
It's not possible to use Wi-Fi calling
Solution 4 of 4: Wi-Fi calling is turned off
When Wi-Fi calling is turned on, you can make and answer calls using a Wi-Fi network when you're in an area with little or no network coverage. To turn on Wi-Fi calling, you need to establish a connection to a Wi-Fi network, select 4G (LTE) as network mode and follow the steps below. You can also visit the EE web page for more information about Wi-Fi calling.
Press the phone icon.
Press the menu icon.
Press Settings.
Press the indicator next to "WiFi Calling" to turn the function on or off.
Press the Home key to return to the home screen.