My iPhone 13 Pro Max show distorted colours after update to iOS 18.5

If Smart or Classic Invert is turning on your iPhone even after you have turned it off though this is strange but you may try some of these...

1. Restart your iPhone: Sometimes, a simple restart can fix issues like this.
   1. Restart the device. That's it.
   2. Still not solved --> Force restart iPhone - Apple Support
2. Reset All Settings: Resetting all settings on your iPhone can help fix software-related issues. Go to Settings > General > Transfer & Reset > Reset > Reset All Settings. This will reset all your settings to default, but it won't erase any of your data. All settings—including network settings, the keyboard dictionary, the Home screen layout, location settings, privacy settings, and Apple Pay cards—are removed or reset to their defaults. No data or media are deleted.
   1. Reset All Settings: Return iPhone settings to their defaults - Apple Support:- Return iPhone settings to their defaults
   2. You can return settings to their defaults without erasing your content.
   3. If you want to save your settings, back up your iPhone before returning them to their defaults. For example, if you’re trying to solve a problem but returning settings to their defaults doesn’t help, you might want to restore your previous settings from a backup.
3. Update your iPhone: Make sure your iPhone is running the latest version of iOS. Go to Settings > General > Software Update and check for any available updates.There are only 2 ways to update an iOS/iPadOS. Know how to...
   1. Update Over-the-Air (OTA) —> Update your iPhone or iPad - Apple Support (IN)
   2. Update using iTunes/Finder —> Update your iPhone, iPad, or iPod touch - Apple Support (IN)

If none of these steps work, it's possible that there is a hardware issue with your iPhone's display. In this case, you may need to contact Apple support or visit an Apple store for further assistance.

Probably you are using Smart or Classic Invert?

Please see the pic below

It's not always the iOS update's fault!  Many things can cause phone problems.  If you tell people you think it's an iOS update, it might make it harder to fix or find a solution for the real issue.

Remember, the right question often leads to the solution!

Was/Is your device Jailbroken? If that's the situation, please be informed that attributing the issues to iOS updates may not be accurate.

iOS updates aim to enhance user experience, boost security, and fix bugs rather than disrupt core features. The majority of the issues after updates might stem from underlying, unmentioned factors. Updates won't typically alter personal data but may refine settings or features. Backup before major updates for safety. Review Apple's update details and backup advice for a smooth process.

Kindly consider checking your settings and addressing any device issues before attributing the issue to external factors. This could be a pure coincidence that the iOS update affected the iPhone functions.

Before initiating a standard iOS update, it's advisable to create a backup. Have you completed this step? If yes, proceed with the restoration from the backup.

See what each update does: About iOS 18 Updates, About iOS 17 Updates, About iOS 16 Updates, About iOS 15 Updates, About iOS 14 Updates, About iOS 13 Updates, About iOS 12 Updates, and so on...