What’s going on in my phone?

Two reasons

1. You had a non Apple shop fit a new screen
2. The screen had developed a fault.

Only option 2) gives you the option to have Apple look at it.

First try a Forced restart

https://support.apple.com/guide/iphone/force-restart-iphone-iph8903c3ee6/ios

If no better

You should arrange a repair

https://support.apple.com/iphone/repair/service

Anything other than Screen or Battery may be a replacement phone and the price is in the article.

You can see additional service information within the following article:

Prepare your iPhone for packing and shipping

if it was me then I would reach out to apple

This is a user helping other users with tech questions

forum, you are not addressing apple here  just  fellow users

you can try contacting apple Get Support (apple.com)

and or give them feedback Product Feedback - Apple

Hi,

Sorry to hear you are having issues with your iPhone.

That error message is given due to the display currently being used for the device is not the same display that was created or supported for that device. In other words, the ‘part’ (display) for the product is not the ‘correct part’ that product should be using, which is a genuine Apple display, created solely for compatibility with that product.

This tends to happen if you had your iPhone repaired at a third-party repair location instead of at the ARS or an AASP.

The third party repair location should still be using genuine Apple parts for the Apple products it is providing service for, but, some places do not like to repair users devices the correct way.

This results with a cheap, incompatible display being placed on the product, the error message that follows, as well as issues with touchscreen functionality.

If you have had your device repaired recently, i would recommend returning to that location and resolving this issue, as they have repaired your device improperly.

If you have never had service on this product, contact Apple Support. They will be able to run diagnostics and confirm from there.

Hope this helps!

It can also result from a spontaneous failure of a genuine part as I stated above.