agFM\grubfm requires that the file extension is lowercase only (.xml) – please do not use any uppercase letters for the file extension.
A file extension of .XML will be ignored by agFM\grubfm.
Your .xml file must be in the same folder as the .iso file. Any folder can be used for the .iso and .xml files but it is best to use the standard sub-folders which are used by E2B and are located under the \_ISO\WINDOWS\ main folder – e.g. \_ISO\WINDOWS\WIN10.