Why I can’t update iOS 16.6

You can try it using iTunes on windows 10 or latest

Update software on iPhone, iPad, or iPod touch in iTunes on PC

Using iTunes, you can update software on your iPhone, iPad, or iPod. 

1. Connect your device to your computer.
2. You can connect your device using a USB or USB-C cable or a Wi-Fi connection. To turn on Wi-Fi syncing, see Sync iTunes content on PC with devices on Wi-Fi.
3. In the iTunes app  on your PC, click the Device button near the top left of the iTunes window.
4. 
5. Click Summary.
6. 
7. Click Check for Update.
8. To install an available update, click Update.
9. 
   

Important: Before disconnecting your device from your computer, click the Eject button .

You need to have a good Service and/or Wi-Fi.

If they are On, turn Off Hotspot & VPN.

Charge the battery > 70%.

Go to Settings -> General -> Software Update -> Download and Install.

See the following Apple articles:

Update your iPhone, iPad, or iPod touch

Update your iPhone, iPad, or iPod touch - Apple Support (IN)

If your iPhone or iPad won't update -> If your iPhone or iPad won't update - Apple Support

You can do the update via PC, see this Apple article: Update software on iPhone, iPad or iPod touch in iTunes on PC

Update software on iPhone, iPad or iPod touch in iTunes on PC – Apple Support (UK)

If you have a Mac see this Apple article: Update your iPhone, iPad, or iPod touch with the Finder

Update your iPhone, iPad, or iPod touch with the Finder - Apple Support

or see: