Stage light in Portrait mode.

There's no way to enable it because iPhone XR has a single-lens camera module.

For the Stage Light you need the second one, that can measure and built the Depth Map.

Add Portrait Lighting

On iPhone X and later, and iPhone 8 Plus, you can use the Portrait Lighting feature to apply studio-quality lighting effects to your Portrait mode images. Choose from Studio Light to brighten facial features, Contour Light for more dramatic directional lighting, Stage Light to isolate your subject in the spotlight, or Stage Mono for stage light in a classic black and white.

You can take a Portrait mode photo with a real-time preview of the lighting effect on your screen. With your Camera app in Portrait mode, swipe between the different lighting effects that appear in the bottom part of the viewfinder. The Portrait mode photo that you take has the lighting effect applied.

You can also change the Portrait Lighting effect of any Portrait mode photo that you've already taken:

1. Open the Photos app, then select the Portrait mode photo that you want to change.
2. Tap Edit. Lighting effects appear in the bottom part of the photo.
3. Swipe the lighting effects to choose the one you want.
4. Tap Done.