Iphone XS Max Green Screen and Random bright flashes

After updating to ios 13.5 my phone’s screen randomly flashes brightly without any reason. Then for some worst occasions, a green screen fills half of the screen! I have to turn off the screen and wait for a while before it’s gone. Is this hardware issue, or software? I never experienced this before and is afraid that this might seriously affect my screen. I never installed any new app, and reset my iphone settings. Still, no luck. Is there a fix to this? I just bought this phone a year ago and it’s brand new.