Trying to generate a map tile cache in ArcGIS Pro, I unchecked the option for "Package for ArcGIS Online | Bing Maps | Google Maps" so that I can use the tile scheme from an existing service. Using the browse button I then navigate to Portal > Living Atlas and select an existing Esri service (World Imagery, World Street Map, World Topographic - I tried a number of them) and get Error 000732. Shouldn't this option allow me to get the tiling scheme from an existing service? The map is saved in the same spatial reference system as the map service.
I also found the same behavior that was noted in this post (Having problems with the Geoprocessing tool 'Create Map Tile Package' ) about not being able to browse to an .xml file. I was able to paste in the path to the .xml file and that worked.