As a process of elimination can you try your sim card in another phone that's not on Android 11 @YROVI
We have seen from others that Calling Over Wi-Fi has glitched but that's usually in connection to the network needing to sometimes send an OTA configuration to reset up the service.
Calling Over Wi-Fi is driven by your sim card so your phone will only use the feature if your sim card / network push it.
Current Phone ~
Samsung Note 20 Ultra 5G SM-N9860_256Gb SnapDragon 865+
Samsung One Ui 3.1/ Android 11.