ListFeatureClasses will search in current workspace, which is r'C:\Vector\20190902'. You need to change it to point at each gdb when listing feature classes.
I dont know why you are listing datasets, are you sure that is what you want?
If you have a structure like this, code below will work:
import arcpy, os
arcpy.env.workspace = r'C:\GIS\...
The bulk of this answer is pulled from http://desktop.arcgis.com/en/arcmap/10.3/tools/modelbuilder-toolbox/iterate-row-selection.htm
This only works in ModelBuilder (not in an arcpy script). It allows you to iterate through a selection of rows based on field values. If you don't select something to group by, then it goes through each row of your input table ...