The sound doesn't change

Hello z1ro4ka.

Thank you for using Apple Support Communities. It sounds like you're unable to make adjustments to your settings. Specifically, you're unable to change your notification sounds on your iPhone. We can understand how this would be an issue. Allow us to investigate this issue and assist in any way we can.

To confirm, is this the only option you're unable to adjust or does this issue occur with other settings you try to change? Ever since this issue started to occur, have you been able to restart your iPhone to see if that helps? This is a simple step to take, but sometimes it can help resolve issues:

Restart your iPhone - Apple Support

If you have any pending updates available for your iPhone, it would be best to install them. Keeping your device fully updated can help resolve various issues and help with overall performance. Just in case, the resources below can guide you through the update process:

How to back up your iPhone, iPad, and iPod touch - Apple Support

Update your iPhone, iPad, or iPod touch - Apple Support

If you're already updated and a restarting doesn't help, you might want to check your restrictions or check if any your device has any configuration profiles installed. They can sometimes prevent you from making adjustments to your device:

Install or remove configuration profiles on iPhone - Apple Support

Use parental controls on your child's iPhone, iPad, and iPod touch - Apple Support

We hope this information is useful. Cheers.