PBI - all data loaded are null

Anonymous It seems like you have extra steps in your Folder query that probably shouldn't be there. Any transformations that you want to add to importing the files should go in your Transform Sample File query, not the Folder query. So, your Folder query should always be something like:

let
    Source = Folder.Files("C:\Users\gdeck\OneDrive\Documents\Folder"),
    #"Filtered Hidden Files1" = Table.SelectRows(Source, each [Attributes]?[Hidden]? <> true),
    #"Invoke Custom Function1" = Table.AddColumn(#"Filtered Hidden Files1", "Transform File", each #"Transform File"([Content])),
    #"Renamed Columns1" = Table.RenameColumns(#"Invoke Custom Function1", {"Name", "Source.Name"}),
    #"Removed Other Columns1" = Table.SelectColumns(#"Renamed Columns1", {"Source.Name", "Transform File"}),
    #"Expanded Table Column1" = Table.ExpandTableColumn(#"Removed Other Columns1", "Transform File", Table.ColumnNames(#"Transform File"(#"Sample File"))),
    #"Changed Type" = Table.TransformColumnTypes(#"Expanded Table Column1",{{"Source.Name", type text}, {"One", Int64.Type}, {"Two", Int64.Type}, {"Three", Int64.Type}})
in
    #"Changed Type"

These two steps seem to not belong:

#"Promoted Headers" = Table.PromoteHeaders(#"Expanded Table Column1", [PromoteAllScalars=true]),
#"Renamed Columns" = Table.RenameColumns(#"Promoted Headers",{{"Speaker data 2021.xlsx", "Source.Name"}}),