This issue has been there for years together now. Multiple users, especially 12 to 14 series had reported green screen issue. I can confirm that because my 13 pro max phone got the green screen issue about 18 months back, luckily for me it was under the one year warranty period and so got the display replaced for free.
Further, when was in the service center I could see a lot of customers queuing up for same issue and many of them were denied free screen replacement because of out of warranty and were asked to pay up.
So to summarize, if you are luckily then your device wouldn’t get the issue. The best thing to do is not to update right now and only update to 17.7
Anyways, the device is not going to get the much hyped AI features which is available even in a basic android phone nowadays ( Apple says neural engine, processor etc.,).
Hard earned money, think about this as well - Compare with Google tensor processor which supports Gemini AI or a Snapdragon processor on Samsung devices in the same or little less price range.
Having said all of the above, should you have updated to iOS 18, my suggestion is you should have waited because of the fact that many users including iPhone 16 users have been reporting multiple issues with iOS 18.
What can you do now? take the device to an Apple care center and not to an authorised service center, I have seen some YouTubers stating that Apple care centers do accept free screen replacement on case to case basis. Best of luck!!!. Come back and reply back in the forum and what your experience in Apple care center was so that other users might also benefit from your experience.