Why is my new iPhone 16 connected to home Wi-Fi but only using mobile data?

New setup from existing iPhone 12 using same Apple ID & network settings. No issue with iPhone 12 & home wifi. The new iPhone 16 connects automatically to existing & previously used wifi networks, but does not make wifi calls nor use wifi to browse or run Speedtest. Have restarted router & iPhone 16 & reset networks on iPhone 16. The wifi connected symbol does not appear, even though the Settings shows it’s connected to the wifi network with a private ip address, etc. And all other iPads & iPhone 8 work fine on house wifi & run Speedtest.

[Re-Titled by Moderator]