I understand why you’d be curious, but in short, there really aren’t any “free” tools that legitimately let you read someone else’s Instagram DMs. Almost every site or app promising this will either try to phish your own Instagram credentials or sneak malware onto your device. Beyond violating Instagram’s Terms of Service, using such tools is typically illegal in many places.
If you genuinely need access—for example, you’re a parent concerned about your child—your safest route is to have an open conversation with them or use Instagram’s official Family Center features. For your own account, Instagram even offers a “Download Your Data” tool so you can see your history securely.
Can you tell me a bit more about what you’re trying to achieve or the risks you’re most worried about? That’ll help me point you toward a more appropriate and legal solution.