The tile packages generated in .tpkx format from ArcGIS 3.6 and uploaded to ArcGIS Online, cannot be used as the basemap on the "Tile package from my organization" option in ArcGIS FieldMaps Designer. However, if the same map is generated as .tpk, can be found with Designer! Previous version (at least 3.4.x) ArcGIS Pro won't have these issues.
