Updated to iOS 15.7 before iOS 16 and no longer see iOS 16

Turn off low power mode. If the update is not reappearing please update via a pc or Mac instead

Update your iPhone using a Mac with macOS Catalina or higher

On a Mac with macOS Catalina or higher, you will use the finder in order to upgrade your iPhone. Make sure to Back up your device before starting the upgrade process.

On a Mac with macOS Catalina or later, you will follow the following steps:

1. Open a finder window
2. Connect your device to your Mac via a lighting to usb A or a lightning to usb c cable
3. Select your device in the left sidebar of the finder window
4. click general, then click check for update
5. Click download and update.
6. If asked, enter your iPhone passcode

Update your iPhone via a Mac running macOS Mojave or earlier, or on a Windows PC

On macOS Mojave or earlier, or on a windows machine, we won't use the Finder to upgrade your iOS

Instead, we will use iTunes. Make sure to Back up your device before doing any update or upgrade to your phone.

1. Open iTunes
2. connect your device to the computer with an lightning to usb a or a lightning to usb c cable
3. Click device button in the iTunes toolbar
4. In the summary tab, click check for update
5. Click download and update, follow The on screen instructions
6. If asked, enter your iPhone passcode.

You should be able to get iOS 16. Try restarting the phone. And you might also try a Forced Restart. No guarantee but worth a try...

Force restart iPhone - Apple Support (CA)

If by chance you have 16 beta installed, try removing it...

How to uninstall iOS or iPadOS beta software - Apple Support

I tried restarting and forced restarting the phone, but not luck, still shows ios 15.7 as ios is up to date

The battery cannot be on Low Power Mode during an update. Yours is. Turn off Low Power Mode.

Phone needs to be charged to at least 50%. 100% would be better.

You also need to turn off Low Power Mode to perform the update once you remove the beta version.