Iphone x screen is green
How to fix iPhone x green screen
Almost certainly a hardware problem.
First make sure you are on ios14.6
After that 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, depending on your warranty or AppleCare+ status.
You can see additional service information within the following article:
Get your iPhone, iPad, or iPod touch ready for service - Apple Support