No, LAS files are not supported in ArcGIS Online. ArcGIS Online Map Viewer is used to visualize 2D maps and does not support 3D map data such as LAS files. LAS datasets contain z-values that cannot be interpolated in ArcGIS Online web maps.
LAS files are however supported in ArcGIS Pro and ArcMap. Refer to ArcGIS Pro: Adding a LAS dataset to the map view and ArcMap: How to display the LAS datasets as a surface in ArcMap for more information.
Alternatively, LAS data can be visualized in Scene Viewer as lidar point clouds. The LAS file is converted to point clouds in ArcGIS Pro before it is published as a cloud scene layer package. To visualize LAS datasets in Scene Viewer, refer to Imagery Workflows: Sharing lidar points for visualization on the web for steps.