iPhone 16 Pro Max: Wi-Fi is on, but displaying 4G

Brand new phone. I checked my settings, my Wi-Fi is on, and the phone shows it is connecting through my broadband router. However, the phone displays 4G rather than the Wi-Fi symbol at the top. I know for sure I am connecting through my Wi-Fi because my broadband speed tests show >450Mbps. If I switch off Wi-Fi and run the speed test on 4G, it shows ~30Mbps. Do you have any ideas on how to fix this so that the Wi-Fi symbol shows on my display rather than 4G? I have restarted the phone several times but no joy.

On top of that, some of my apps, like Facebook, WhatsApp, Quik, etc., report no internet connection, even though I can use Safari to browse the Internet and run broadband speed tests, and my iPhone apps restoration is in progress!