Hello - I have a Galaxy Note 9, and I have "Wi-Fi Calling" under "Connections" selected (toggle switch is blue.)
I just noticed tonight that whenever I call someone, the "Wi-Fi Calling" option gets grayed out during the call. Then when I hang up, it reverts back to the blue.
If I recall correctly from a call to tech support a few years ago, this is normal. It turns gray because it is telling you that Wi-Fi calling is being used, but it turns back to blue when you hang up, telling you that it's ready for another Wi-Fi call.
Trying to remember if I am I correct on this. Can someone let me know? Easy way to test is for you to turn "Wi-Fi Calling" on (toggle switch blue) and then call a friend, and check if it is grayed out during your call.
Thanks!