Please check the bandwidth 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#* and pressing the call button and then selecting the Serving cell info option
Bandwidth on the 2nd and 3rd Screenshots.
See the pic below which is self-explanatory


E, 2G, 3G, 4G, LTE, VoLTE, 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 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 "Cellular and Wireless" section.

Know it here --> All about G, E, 3G, H, H+, 4G, VoLTE, 5GE and 5G symbols ...
