I don’t see a setting for Wi-Fi calls

See the following: Make a call with Wi-Fi Calling - Apple Support

including the excerpt below:

To use Wi-Fi Calling, you need an iPhone 5c or later on a supported carrier.

WiFi calling is a carrier feature.

The option won't appear in Settings (Settings>Phone>WiFi Calling) unless your carrier supports it on the iPhone and the feature is provisioned on your account.