Portrait mode is a fun and powerful computational photography tool included with iPhone 7Plus, 8Plus, X, XR, SX, 11, 11Pro and 11Pro Max.
It simulates the BOKEH effect that many professional portrait photographers like to use. On a DSLR, you’d use a “fast” lens – meaning a lens with a wide aperture. This allows the foreground subject to stand out from the background by making the background blurry.
Portrait Mode is a software version of that effect and it works well – most of the time. But there are times when, for whatever reason, it misfires. If you selected Portrait Mode for one of your pictures and do not like the results, don’t worry. You can undo that decision later.
To turn off Portrait Mode after the fact…

Open the Camera app and select the photo you want to fix OR open the Photos app and select the photo you want to fix.

Tap the edit button in the top right corner of your screen.
At the top of the page, in the center the word PORTRAIT will be highlighted in yellow. (Sometimes it takes a second before this shows up so be patient.)

Once you see the yellow PORTRAIT button, just tap it to turn off the effect. Be sure to hit save and then tap done. Your photo reverts to a standard picture – minus portrait mode.
Image Credits: apple.com.