For those that did not know, ArcGIS Pro has a great built-in workflow for taking feature layers and basemaps offline. This is a workflow we teach in conjunction with the SAR Common Operating Platform so GIS users are "always ready" to respond to no-notice events in their own area where connectivity may be limited.
Documentation: https://pro.arcgis.com/en/pro-app/latest/help/projects/take-a-map-offline.htm

However, one new thing we noticed is the basemaps available via the ArcGIS Pro Basemap Gallery will not work for this process. If you attempt this, it will begin the process, create a folder for the vtpk, but then stop without warning or error.

To fix...
1) Add Data
2) Search for "Basemaps For Export" (you can see these in ArcGIS Online via this Group)
3) Add to map
4) Remove any other Basemaps
5) Follow steps outlined here https://pro.arcgis.com/en/pro-app/latest/help/projects/take-a-map-offline.htm

If anyone from the ArcGIS Pro or ArcGIS Online Team have any additional clarification, please post below!