Even on supported phones, apps may limit resolution or frame rate while two cameras run, because it uses more power and heat. Music Wide Selfie only offers Dual Camera where the hardware supports it.
Dual / Which iPhones can record two cameras at once?
Guide
Which iPhones can record two cameras at once?
Short answerApple's multi-camera capture needs an iPhone with an A12 Bionic chip or newer, which means iPhone XS, XR and later, plus an app that supports it. The built-in Camera app's support varies by model and iOS version.
About Music Wide Selfie
An iPhone camera app in development for people who film themselves. Not released yet; one email when it is.
One email when the app is ready. Nothing else.