There are a few proven ways to monitor Snapchat on an iPhone, each offering different levels of visibility.
One method involves using the device’s iCloud backup. If you have the Apple ID credentials, you can access data that has been backed up, which may include some application data.
Another option is to use the built-in Screen Time features on the iPhone. This allows you to view app usage statistics and set time limits, but it does not show the content of messages.
For more comprehensive tracking, a dedicated spy app is a common solution. This type of monitoring software is specifically designed to capture activities directly from applications, including Snapchat messages and media.