Attribute-driven symbology in web scene layers support Arcade expressions only.
Solution
Change one or more of the transparency, rotation, size, or color visual variables to use an Arcade expression.
- Right-click the layer in the Contents pane and click Symbology .
- In the Symbology pane, click the Vary symbology by attribute button .
- Expand the visual variable heading and click the Set an expression button next to the field.
- In the Language drop-down menu, click Arcade and click OK.
- In the Sharing pane, click Analyze.
The error is resolved.