Smart HDR doesn’t seem to work

Hello and welcome to Apple Support Communities, Rafael!

I understand expected the HDR feature to be used when shooting this photo. I'd be happy to clarify what may be happening.

You may have your camera set to automatically detect the need for HDR. You would have to change this option in Settings > Camera to always have the choice enabled.

Read more about HDR here: Use HDR on your iPhone, iPad, and iPod touch

"Take an HDR photo

1. Open the Camera app on your iPhone, iPad, or iPod touch.
2. Tap HDR and make sure it's set to Auto or On.
3. Frame the photo.
4. Tap .
5. 
   
6. When you take an HDR photo, your device saves two versions of the image to the Photos app. One with HDR and one without. That way you can compare the two and use the one that you like most. To save space, you can turn off this feature and keep just the HDR version in your library. Go to Settings > Camera > Keep Normal Photo and swipe to turn off.

If you set HDR to On, your device captures an HDR image every time you take a photo. If you set HDR to Auto, your device determines whether or not each photo would look better with or without HDR."

I hope this clears things up for you.

Have a great day!