You will need to convert the extruded polygons to multipatch and then you can publish the scene from Pro 2.1 to create a web scene with 3D Object scene layers or you can uploade a zipped gdb of the multipatch feature class to create a feature layer and then you can publish a scene layer from that feature layer. You can also package the multipatch feature class into a scene layer package and upload that to AGOL like a tpk and create a scene layer.
We do have plans to allow extrusion by attribute but it will not be in the upcoming release.