Unknown accessing microphone?

Wondering if you have installed third-party (non-Apple) apps or accessories that have access to the microphone.

You can: Control access to hardware features on iPhone - Apple Support

Eg: says:

Review or change access to the camera, microphone, and other hardware features

1. Go to Settings  > Privacy & Security.
2. Tap a hardware feature, such as Camera, Bluetooth, Local Network, or Microphone.

The list shows the apps that requested access. You can turn access on or off for any app on the list.

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Else see: How Safety Check on iPhone works to keep you safe - Apple Support

If needed: How to: Report a security or privacy vulnerability - Apple Support

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If you want to check on sharing you may have set up and be allowing:

How to use Shared Albums in Photos on your iPhone, iPad, and Mac - Apple Support

Share files and folders in iCloud Drive on iCloud.com - Apple Support

or

To leave (or remove someone from) family sharing:

Leave Family Sharing - Apple Support

All the best :-)

Thank you kindly for taking the time to reply, for checking through those suggestions, and for sharing your experience with the community. :-)