Dataset Theme Issue

In watching Stephen Wolfram introduce Vers. 12.3, I installed the upgrade from 12.2 and executed the following statement as he did in his presentation:

In[9]:= Dataset[IdentityMatrix[6], DatasetTheme -> "AlternatingColumnBackgrounds", LightGreen]

However, unlike him, I see the following output in which the return is merely the list of the 6 by 6 identity matrix rather than the expected visualization seen in his presentation, but with the standard lightgreen color box being converted to its defining RGB color.

Dataset[{{1, 0, 0, 0, 0, 0}, {0, 1, 0, 0, 0, 0}, {0, 0, 1, 0, 0, 0}, {0, 0, 0, 1, 0, 0}, {0, 0, 0, 0, 1, 0}, {0, 0, 0, 0, 0, 1}}, DatasetTheme -> "AlternatingColumnBackgrounds", RGBColor[ 0.88, 1, 0.88]]

The frontend reports no errors as to the synatax.

What am I missing here to make this work as expected? Is there a hidden option value or environmental variable that needs to be set properly before execution to succeed?

Is this a bug?