Black border around screen on iPhone SE 3rd gen after iOS 18.4 update

I updated my iphone SE 3rd gen to ios 18.4. I now notice there's an annoying black border around the edge of the whole screen, meaning the aspect ratio of the screen is incorrect, and the screen isn't full sized anymore. This wasn't an issue before I update the iOs.

I checked Zoom and accessibility and that didn't help. I also restarted the phone.

This seems like a glitch that Apple has caused. Is there any way for me to fix this in settings, or do I just have to accept that a software update that's supposed to improve experience has now worsened it

[Re-Titled By Moderator]