Why is it that my iPhone isn’t showing battery percentage?

With iOS 16, the battery percentage option is now available on iPhones with a notch except for iPhone 12 mini, ‌iPhone 13‌ mini, iPhone 11 (regular), and iPhone‌ XR.

To view Battery Percentage on any other phone with the Face ID "notch" at the top of the screen open the Control Center by dragging down from the battery icon, or add a battery widget to your Home screen. If you examine the status bar at the top of the screen you will observe that there is no room to put the battery percentage.

See→Use widgets on your iPhone and iPod Touch

What model phone do you have?

I already answered your question for any phone with Face ID. If there is no switch to show Battery Percentage on the screen shot you posted then you can’t display battery percentage in the status bar. There WILL be a switch for any phone with Touch ID. And I will repeat what I posted, emphasized this time:

With iOS 16, the battery percentage option is now available on iPhones with a notch except for iPhone 12 mini, ‌iPhone 13‌ mini, iPhone 11 (regular), and iPhone‌ XR.

From a previous reply from Lawrence Finch:

With iOS 16, the battery percentage option is now available on iPhones with a notch except for iPhone 12 mini, ‌iPhone 13‌ mini, iPhone 11 (regular), and iPhone‌ XR.

So, the iPhone 11 does not display battery percentage. Apple has not indicated whether it might be possible to add this option in the future.