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Not completely sure but this may mean this feature is not provisioned by your mobile operator.
For example - I don't have the WiFi calling option available in Settings > Network & internet > SIMs > select the desired SIM here. As you can see in my previous post - it may be because it is not provisioned for me (Voice over WiFi: Unavailable).
So, on your report, I can see "Voice over lte unavailable", assuming that's why you can't see it in your network settings.
Do you have a chance, try asking the carrier's support about 4G/LTE. Sometimes they need to reset/reprovision the things on their end.
Good luck!