Regarding AGOL (or Portal?) layers like this: Digital Raster Acquisition Project Eastern Ontario (DRAPE) 2008 - Web Map Service

I can download a .PITEM or .PITEMX file that contains the layer. As far as I can tell, those files can only be opened as a new project/.APRX in ArcGIS Pro. I don't want to create a new project; I want to add the layer to an existing project.
Since .PITEMX files can't be added to an existing project, I'm wondering if downloading a .LYRX file would be better, since.LYRX files can be added to an existing project.