AudioManager.cs

using System.Linq;
using Godot;
using Godot.Collections;

public partial class AudioManager : Node
{
    // ** needed sounds **
    // Music
    // shoot
    // die
    // enemy die
    // fuel empty
    // Player Die
    // Player Fuel Collected
    // Player Hit

    [Export] private AudioBusLayout _audioBusLayout;
    [Export] private AudioStreamPlayer _musicStreamPlayer;
    [Export] private int _maxPolyphony = 10;

    private float _masterVolume = 0.5f;
    private float _musicVolume = 1f;
    private float _soundVolume = 1f;

    private Dictionary<SoundResource, AudioStreamPlayer> _sfxStreamPlayers = new();


    public override void _Ready()
    {
        GameEventsManager.Instance.GameStarted += OnGameStarted;
        GameEventsManager.Instance.UpdateSoundSettings += OnUpdateSoundSettings;
        GameEventsManager.Instance.PlaySfx += OnPlaySfx;
        GameEventsManager.Instance.StopSfx += OnStopSfx;
        GameEventsManager.Instance.PauseGame += OnGamePaused;
        GameEventsManager.Instance.EmitGetSaveData(OnGetSavedData);
        CallDeferred(MethodName.EmitInitialSoundSettings);
    }

    private void OnGamePaused()
    {
        foreach (var kv in _sfxStreamPlayers)
        {
            var sfx = kv.Key;
            GetSfxPlayer(sfx).Stop();
        }
    }

    private void OnStopSfx(SoundResource sfxSoundResource)
    {
        var sfxPlayer = GetSfxPlayer(sfxSoundResource);
        if(sfxPlayer.Playing) sfxPlayer.Stop();
    }

    private void OnPlaySfx(SoundResource sfxSoundResource)
    {
        PlaySfx(sfxSoundResource);
    }

    private void PlaySfx(SoundResource sfxSoundResource)
    {
        var sfxPlayer = GetSfxPlayer(sfxSoundResource);
        sfxPlayer.Play();
    }

    private AudioStreamPlayer GetSfxPlayer(SoundResource sfxSoundResource)
    {
        AudioStreamPlayer audioStreamPlayer;

        AudioStreamPlayer player;
        _sfxStreamPlayers.TryGetValue(sfxSoundResource, out player);

        if (player == null)
        {
            audioStreamPlayer = CreateNewAudioStreamPlayer(sfxSoundResource, AudioBusIndexes.SfxBusName);
            _sfxStreamPlayers.Add(sfxSoundResource, audioStreamPlayer);
            AddChild(audioStreamPlayer);
        }
        else
        {
            audioStreamPlayer = player;
        }

        return audioStreamPlayer;
    }

    private AudioStreamPlayer CreateNewAudioStreamPlayer(SoundResource soundResource, string busName)
    {
        var audioStreamPlayer = new AudioStreamPlayer();
        audioStreamPlayer.Stream = soundResource.AudioStream;
        audioStreamPlayer.Bus = busName;
        audioStreamPlayer.MaxPolyphony = _maxPolyphony;
        return audioStreamPlayer;
    }

    private void OnGetSavedData(SaveData saveData)
    {
        _masterVolume = saveData.MasterVolume;
        _musicVolume = saveData.MusicVolume;
        _soundVolume = saveData.SfxVolume;
    }

    public override void _ExitTree()
    {
        GameEventsManager.Instance.GameStarted -= OnGameStarted;
        // GameEventsManager.Instance.PauseGame -= OnGamePaused;
        // GameEventsManager.Instance.ResumeGame -= OnGameResumed;    
        GameEventsManager.Instance.UpdateSoundSettings -= OnUpdateSoundSettings;
    }

    private void OnUpdateSoundSettings(float masterVolume, float musicVolume, float sfxVolume)
    {
        _masterVolume = masterVolume;
        _musicVolume = musicVolume;
        _soundVolume = sfxVolume;

        AudioServer.SetBusVolumeDb(AudioBusIndexes.GetMasterBusIndex(), Mathf.LinearToDb(_masterVolume));
        AudioServer.SetBusVolumeDb(AudioBusIndexes.GetMusicBusIndex(), Mathf.LinearToDb(_musicVolume));
        AudioServer.SetBusVolumeDb(AudioBusIndexes.GetSfxBusIndex(), Mathf.LinearToDb(_soundVolume));
    }

    private void EmitInitialSoundSettings()
    {
        // GetInitialAudioLevels();
        GameEventsManager.Instance.EmitInitialSoundSettings(_masterVolume, _musicVolume, _soundVolume);
    }

    private void GetInitialAudioLevels()
    {
        var masterVolumeDb = AudioServer.GetBusVolumeDb(AudioBusIndexes.GetMasterBusIndex());
        var musicVolumeDb = AudioServer.GetBusVolumeDb(AudioBusIndexes.GetMusicBusIndex());
        var soundVolumeDb = AudioServer.GetBusVolumeDb(AudioBusIndexes.GetSfxBusIndex());

        _masterVolume = Mathf.DbToLinear(masterVolumeDb);
        _musicVolume = Mathf.DbToLinear(musicVolumeDb);
        _soundVolume = Mathf.DbToLinear(soundVolumeDb);
    }

    private void OnGameStarted()
    {
        _musicStreamPlayer.Play();
    }

    public static class AudioBusIndexes
    {
        public const string SfxBusName = "Sfx";
        public const string MusicBusName = "Music";
        public const string MasterBusName = "Master";

        public static int GetMasterBusIndex()
        {
            return GetBusIndex(MasterBusName);
        }

        public static int GetMusicBusIndex()
        {
            return GetBusIndex(MusicBusName);
        }

        public static int GetSfxBusIndex()
        {
            return GetBusIndex(SfxBusName);
        }

        private static int GetBusIndex(string busName)
        {
            return AudioServer.GetBusIndex(busName);
        }
    }

    public class SfxSounds
    {
        public static string PlayerFireBlaster = "PlayerFireBlaster";
    }
}

This is added to a scene of type Node only and added as AutoLoad in Godot.