I have some colors corresponding to points. How to render point clouds and set colors for each point

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4

vtkPolyData does have setPoints(), see here (accessors is provided thanks to this).

You also need to set vertices for your point cloud (i.e. polyData.setVerts(...)).
And to assign a color at each point:

const colors = new Uint8Array(points.getNumberOfPoints());
// ...fill colors here...
const colorsDataArray = vtkDataArray.newInstance({name: colors, values: colors});
polyData.getPointData().setScalars(colorsDataArray);