This issue stems from the Razer Chroma app. When I close the app, Alt works. However, once the app is launched and in one of the Fn + F9 modes, Alt becomes unusable, or pressing Alt causes a series of jumps between different screens. This problem is likely a bug in the Razer Chroma app. Razer, please fix this as soon as possible; otherwise, my keyboard, which supports RGB, will be forced to uninstall the Razer Chroma app due to this Alt bug.
(Note: Fn + F9 does not affect some modes.)