The appearance of a green line on the screen of your iPhone 13 Pro Max could be due to a few different reasons. It might be a software glitch, especially if it appears intermittently and your phone hasn't suffered any physical damage. Here are some steps you can try to resolve the issue:
https://www.bing.com/search?form=SKPBOT&q=Restart%20Your%20iPhone: Sometimes a simple restart can fix temporary display glitches.https://www.bing.com/search?form=SKPBOT&q=Update%20iOS: Check for any available updates for your iOS, as newer versions may contain fixes for such issues.https://www.bing.com/search?form=SKPBOT&q=Reset%20Settings: Try resetting all settings on your iPhone. This won't erase your data but will reset system settings to their defaults.https://www.bing.com/search?form=SKPBOT&q=Force%20Restart: Perform a force restart on your iPhone by quickly pressing and releasing the volume up button, then quickly pressing and releasing the volume down button, followed by pressing and holding the side button until the Apple logo appears.
If the green line persists after trying these steps, it could be indicative of a hardware problem. In such cases, it's best to contact Apple Support or visit an authorized service provider for further assistance green screen after updating to 16.4.1 - Apple Community https://discussions.apple.com/thread/254818597. They can perform a diagnostic and provide the appropriate service options. Remember to back up your iPhone before any service appointment.