Unable to see Voice over 5G standalone toggle

Please check the Deployment Type (SA or NSA) that you are getting. Disable WiFi before running this Field Test.

You may check the current LTE band/5G/4G/3G by dialing *3001#12345#* pressing the call button and then selecting the Serving cell info option

Deployment Type: NSA or SA is visible: JIO is SA and Airtel is NSA (Deployment type on the 2nd Screenshot)

Bandwidth on the 2nd and 3rd Screenshots.

See the pic below which is self-explanatory

E, 2G, 3G, 4G, LTE, VoLTE, and 5G all are Carrier Specific features. Contact your Carrier (Cellular Service Provider), the agency that issued the SIM / eSIM to you. About the LTE options on your iPhone - Apple Support (IN)

See the Pic below and the explanations thereof

The pic below is self-explanatory

However, iPhone model-specific feature is listed here --> Identify your iPhone model - Apple Support . and tap on "See the Technical Specs for Model "XXXXXX" under each model and Scroll down to the "Cellular and Wireless" section.

Please understand this...

5G (Fifth Generation) mobile technology has two deployment options: Stand Alone (SA) and Non-Stand Alone (NSA).

1. Non-Stand Alone (NSA) 5G: NSA 5G technology uses the existing 4G LTE network infrastructure as an anchor to establish a connection between the user equipment (UE) and the 5G radio access network (RAN). In NSA mode, the 5G network relies on the 4G core network to provide services to the end user. NSA technology is a transitional mode of deployment and allows for faster implementation of 5G networks by building upon existing 4G infrastructure.
2. Stand Alone (SA) 5G: SA 5G technology is a completely independent network that does not rely on the 4G network for connection establishment between the UE and the 5G RAN. In SA mode, the 5G network has its own core network and provides end-to-end services, including control plane and user plane functions. SA 5G technology is designed to fully realize the benefits of 5G, including high-speed data transfer, low latency, and massive machine-type communication.

Overall, SA 5G is considered to be the more advanced and desirable deployment option for 5G networks, while NSA 5G allows for a more gradual transition to the new technology.