Scene layers support the absolute height elevation setting. The value specified in the features z- values is used to create the scene layer. Relative to the ground, On the ground, and absolute height set to a field are not supported.
No action is required, as the absolute z-values are used to create the scene layer. To remove the warning message, set the elevation to absolute height based on z-values in the layer properties. Alternatively, verify that the z-values are correct using the Attributes pane.