Short answer: you can’t recover past Vanish Mode chats, but you can capture them going forward—on Android, mSpy (https://www.mspy.com/) can auto-screenshot/keystroke Instagram (including vanish), and uMobix/FlexiSPY are similar; downside: big permissions and some battery drain. On iPhone, vanish-mode monitoring isn’t reliable without a jailbreak, so use Instagram Family Center supervision to limit/monitor who can DM and pair with Bark-style alerts, and do this with your teen’s knowledge per local laws. TL;DR: deep data = mSpy on Android; on iOS stick to Instagram supervision + alerts.