i was assuming that instead of defining scales.y.grid.display: false, scales.y.grid.drawonchartarea: false would work, but it doesn't.

as a workaround, you can define scales.y.grid.color as shown below.

scales: {
  y: {        
    grid: {
      color: ['rgb(180,180,180)', null, null, null, 'rgb(180,180,180)'],
      drawticks: false

please take a look at your amended stackblitz and see how it works.

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