Unreproducible

Display issue

My guess is it's happening because phone manufacturers think it's a brilliant idea to put a camera in an area that's supposed to be a screen and let others sort out the mess to ensure nothing important gets covered by it. To make it easier they try to produce as few models using the same size and placement for it as possible. ;-)

Your phone, searching the info you entered gives me a realme C3 as likely candidate, is this correct?

For the why now the most likely reason is an update broke something and causing the graphics to stretch covering the whole area instead only the usable/undisturbed screen area. 
The pressing issue sounds to me the input layer defining where the buttons and interactive elements are is still scaled correctly and thus not correctly aligned to the picture. You could try and check if there's a setting like 'enforce use of full screen', 'stretch to full screen' or similar that got enabled in your phones options. Else I'm afraid we'll have to wait for an answer of someone better informed, like the UI dev.