If the microphone problem arose after you installed updates on your iPhone 8, it could be considered a post-update issue that has to be resolved. Because certain updates supersede your current settings, it's likely that some audio or other important parameters were modified, resulting in this conflict. To exclude this as a possible trigger, try resetting all settings on your iPhone 8. But keep in mind that doing so will also remove your current settings configurations and restore them to their default state. If you're comfortable with it, go ahead and try this reset.
To reset all of your iPhone 8's settings, navigate to Settings-> General-> Reset-> Reset All Settings. Enter the proper passcode if required, then hit the option to confirm reset.
There will be no data loss because no data will be touched during the process.
