VoLTE will work over 5G (and sometimes over 3G in esoteric configurations). It is very data centric, even using SIP for call control. A rule of thumb is, any time you have a data connection, VoLTE can be used.
This is why Wi-Fi Calling and VoLTE took off at roughly the same time. Once you can route calls as data, you can offer it over both cellular and Wi-Fi. (Wi-Fi Calling has an additional outer IPsec layer, but it is the same "guts" inside the tunnel.)
My understanding is that VoLTE/VoNR/VoWiFi is all the same 3G era IMS stack (with updates since then) and thus SIP over IP over either GPRS Tunnel Protocol over low level radio interface or WiFi
This is why Wi-Fi Calling and VoLTE took off at roughly the same time. Once you can route calls as data, you can offer it over both cellular and Wi-Fi. (Wi-Fi Calling has an additional outer IPsec layer, but it is the same "guts" inside the tunnel.)