Hello Powerchip13,
Thanks for visiting the Apple Support Communities and asking about Portrait mode on your iPhone SE.
This article mentions that the device does have Portrait mode: Use Portrait mode on your iPhone - Apple Support
"These iPhone models support Portrait mode: iPhone 12, iPhone 12 mini, iPhone 12 Pro, iPhone 12 Pro Max, iPhone SE (2nd generation), iPhone 11, iPhone 11 Pro, iPhone 11 Pro Max, iPhone XR, iPhone XS, iPhone XS Max, iPhone X, iPhone 8 Plus, and iPhone 7 Plus."
But it seems to only be possible when the device detects a person's face as mentioned in the same article above:
"With iPhone XR and iPhone SE (2nd generation), the rear-facing camera must detect a person's face to take a Portrait mode photo."
Thank you and have a wonderful day.