Can’t update my iPhone 12 to iOS 16.5.1

You cut off the top of your phone's display but I am presuming you are not connected to the Internet. Connect to WiFi or use cellular. To learn how to connect your device to a Wi-Fi network, including open, secure, public networks, and networks that you've connected with in the past, click here --> Connect to Wi-Fi on your iPhone, iPad, or iPod touch - Apple Support

 Connect to a Wi-Fi network

1. From your Home screen, go to Settings > Wi-Fi.

2. Turn on Wi-Fi. Your device will automatically search for available Wi-Fi networks.

3. Tap the name of the Wi-Fi network that you want to join. Before you can join the network, you might be asked to enter the network's password or agree to terms and conditions [ Use captive Wi-Fi networks on your iPhone or iPad - Apple Support ].

16.5.1 is the highest there is. If you are seeing reference to downloading an (a) version, that was temporarily withdrawn by Apple though the notice may still appear.

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