Regarding resources like Ontario GeoHub's Open Web Map Services > Eastern Ontario > AGOL page:
There is an option in the Open in ArcGIS Desktop picklist > Open in ArcGIS Pro that will download a .pitemx file.
When I google pitemx, I don't see any Esri documentation pages in the results, other than a Workflow Manager Server page that doesn’t really help me.
Could a section be added to the docs that explains what a .pitemx file is, how it can be used, and other specs? I am able to open the file in ArcGIS Pro 3.3.0. And I can save it as a .lyrx if wanted. But beyond that, I don't know what I'm looking at.
ArcGIS Online is not my area of expertise.