The only recommended and legal way to get v0.18.4.1 is through Steam. However, Steam will automatically update your game to the current version. To access an older version like v0.18.4.1, you may need to look into Steam's "Betas" or "Depots" features, though this is generally not recommended for average users due to the risk of installing outdated and potentially unstable software.
Fixed a bug where turbocharger spooling sounds would persist even after the engine stalled. BeamNG.drive v0.18.4.1
If you want to keep v0.18.4.1 and also play current versions: The only recommended and legal way to get v0