Yeah, there appears to be two types of .pitemx files, those automated kind with file names of item.pitemx, and those that are actual packages people create by exporting them from Pro and uploading them to AGOL (or your local portal). Those latter kinds seem to work, which is what I was referring to when I wrote that. I always get those item.pitemx to open Pro but they don't extract anything into Pro.
But, that's probably because that's a vector tile layer, and you won't actually download the contents to your computer. VTL's are something you would just add to your Pro map by using the Add Data option. For that OSM VTL you provided, I just searched the Living Atlas in Pro Portal from the Add Data option for "OpenStreetMap", and bam, there are all your OSM VTL options to chose from to add to your map.
I am running ArcPro 2.4. This does not open the Sea Level Rise Innundation pitem files located here. Any idea why not ? https://willis.maps.arcgis.com/home/item.html?id=cfeb90feb74343f3b0328e13184ee9b5
If you're experiencing #BUG-000122065 Opening an ArcGIS Online Item in ArcGIS Desktop (ArcGIS Pro) when an instance of Pro is already running, creates a new instance of Pro instead of adding the item to the existing instance be sure to contact TS and attach yourself to the bug in hopes that it will soon be corrected.