This is default iOS behavior and GeForce NOW cannot change it.
This is caused by a Webkit issue in the Safari browser. We are working with Apple to resolve this for future Safari update. We recommend you to disable mic if you do not plan to use it.
1. While streaming a game, tap the screen to show the on-screen control menu in the upper left of the screen, if it’s not already visible.
2. Expand the menu, if needed, by tapping on the arrow.
3. Tap the mic icon to toggle between enabled and disabled.