MapViewer Symbology Clustering with Pie Charts based on ArcadeExpression not available

[SebastianKrings]

Hi,

In ArcGIS Online and AGE I can do Clustering with PieCharts.
But this only seems to work in combination with a field but not with an ArcadeExpression.

But this does not work when I create an expression instead using a field.

I am using the layer strs_schools from ArcGIS Online.
When using the field speed_limit for styling:

I can choose Pie-Clustering:

When creating an expression only returning the fields value:

$feature.speed_limit

Then I do not get the option for PieCLusters:

Any Idea whats going wrong here?