Help with fullscreen app

[Android Central Question]

I am currently running a Pocophone F1, to test it out. I am very happy with it, other than the cropping in some apps. The main issue i have, is that Snapchat won't take 16:9 pictures. All my friends are getting Images with black bars at the sides, which i really don't like. I have tried to disable full screen mode, but the 'turn on, turn off' icon is greyed out. Anyone know how to fix this?