iPhone XS Max huge lags

[Cianthy]

Hello everyone, 

 

So my brother's XS Max screwed up after the last update (12.3.1) which kinda made it unusable. We tried hard reset (reset to fabric settings) soft reset, everything, its the same. A freshly reset phone without any app installed is lagging. When you click contacts it takes few seconds to load, when you swipe down the notification screen you can see it moving step by step, everything is really laggy. After we loaded apps, if you open say facebook messenger, its white screen for a good 5-10 seconds until it shows up.

 

Tried googling everything, unable to find a fix. Does any of you have any idea what I might try before going to apple store and service it?

 

Thank you all for your time.

[Radioactive Snowman]

I would just bring it to apple, you seem to have already tried everything