wifi calling option not showing on iPhone SE after iOS 14.4 update

SMS, MMS, WiFi Call, Call Forwarding, Call Waiting, Call Merge, Conference Call, Hotspot, Voice Mail (Visual or Normal) all are Carrier Specific features. Contact your Carrier (Cellular Service Provider), the agency who issued the SIM / eSIM to you.

First try taking out the SIM and put it back. May trigger a carrier update.

Also check Settings, General, About and see if an update is pending.

Yay!