The PNG reader only reads the density when the ResolutionUnits are set.
And there is a bug when you read magickImageDestination.ResolutionUnits. It will show PixelsPerInch because you set it to that. But the value will always be PixelsPerCentimeter for a PNG image. The next release will return the correct value.
magickImage1.ResolutionUnits = Resolution.PixelsPerInch;