Why is my camera portrait stuck on 3x?

You may try some of these steps...

1. Sometimes, a simple restart can resolve temporary software glitches. Turn off your iPhone, wait for a few seconds, and then turn it back on.
   1. Restart the device. That's it.
   2. Still not solved --> Force restart iPhone - Apple Support
2. Go to the Settings app on your iPhone, select "Camera," and ensure that the front camera is not disabled or restricted in any way. Photography using iPhone - Apple Community
3. Reset all settings: If the issue persists, you can try resetting all settings on your iPhone. This will not erase your data but will reset all personalized settings to their default values. Go to Settings > General > Transfer & Reset > Reset > Reset All Settings and confirm the action. Note that you will need to reconfigure your settings afterward. 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.
4. If the problem is specific to certain camera apps, make sure you have the latest updates installed, or try reinstalling the problematic apps.
   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)

This is what happened to my 13 Pro Max. Took it to a licensed repair shop and they said the only way to fix it is to replace the camera. But it is obviously a software bug since it is impossible to damage it in that particular way.

I think it’s a bug made by Apple and sent with an update to make you buy a new phone.