Hi! Let me help you.
Go to Settings > Privacy & security > Microphone, and make sure "Microphone access" is turned on and that the Camera app specifically has permission under the list of allowed apps.
Next, check your Sound settings. Go to Settings > System > Sound, and look under Input to see if your microphone is selected as the default recording device and isn't muted or set to a very low volume.
It's also worth checking the Camera app's own settings. Open the Camera app, click the gear icon, and confirm there's a microphone toggle turned on if your version of the app has one.