Is this gone on iOS 16

Not as far as I know

The article above says

"You can use Notify When Left Behind on an iPhone with iOS 15 or later, iPad with iPadOS 15 or later, Mac with Apple Silicon, and with Find My items. For AirPods Pro, AirPods Max, and AirPods (3rd generation), you need an iPhone 12 or later. "

You understand that you can only set it for a device other than the one you are using to set it up.

So I can only set up Notify when left behind for my iphone 7 when I am in Find My in my iPhone 12.

Theres no point sending my iphone 12 a message that I left my iphone 12 behind.

No it’s still there. Are you experiencing an issue?

Using Find My on iphone 12

MBA

iPhone 12

Are you on iphone 14 trying to turn it on for the iphone 14? If so read my reply again