Why is my microphone not working on apps, but it works on my camera and siri?

Did you make sure, that in Settings/Privacy & Security/Microphone, those 3rd party apps are allowed to use the microphone?

About privacy and Location Services in iOS, iPadOS, and watchOS - Apple Support

Did you already force restart your iPhone?

Force restart iPhone - Apple Support

Any restrictions set up in the settings for Screen Time?

Did you test your microphone, using the voice memo app?

Have a look at the troubleshooting in this article:

If the microphones don't work - Apple Support

In that case you should contact Apple Support to discuss your service options.