Line layer

C# type: LineLayer.

Key paint: LineColor, LineWidth, LineOpacity, LineDasharray, LineGradient, LineLayerOpacity.

await map.AddLayer(new LineLayer
{
    Id = "route",
    Source = "route",
    Paint = new LineLayerPaint { LineColor = "#e74c3c", LineWidth = 4 },
});

See line layer example.