Audio always comes last, but that doesn’t mean it’s a less important component than others.
As for the other fields, the sound within a game requires the intervention of a specialist and dedicated tools, often external to the game engine itself.
Audio has a considerable task, it is meant to complement our sensations and must move in step with the visual effects.
It has to be adequate to the realization of the game, it also wants to send a message. It is not enough to put the usual epic music in all moments and sad music in others. The work of sound designers and composers is anything but simple, you have to know how to use it. You feel when you are neglected.
Unity has an internal library of audio-related commands that can be managed independently on individual game objects. Or manage them centrally by creating scripts that act as audio managers.
The creation of audio files is handled externally but there are middlewares like FMOD that can also be directly connected to Unity even during debugging.