The Spatial Reference / Projection Defaults to WGS Web Mercator: 102100 (3857) when you create a Layer in AGOL. This is not always preferred when you want to track shape lengths or areas, because this default projection it will track these fields in meters. That is just one example.
To have our preferred projection on a Feature Layer, I have to create all of our layers in ArcGIS Pro where I have the option to select a Spatial Reference / Projection, and then I share it to AGOL where our local state plane is set to the Feature Layer: 102723 (3735).
Having the option in AGOL or Portal to select a Spatial Reference would benefit a lot of individuals who are not using or are not able to use desktop applications. This would allow organizations to have uniformity in layer spatial references and not have a mix of Web Mercator and the desired spatial reference.
