Identify Duplicates and Create Column Identifying Them

You may try Power Query fuzzy match playing with threshold

let

    threshold = Excel.CurrentWorkbook(){[Name="Threshold"]}[Content][Column1]{0},

    Source = Excel.CurrentWorkbook(){[Name="Table1"]}[Content],
    DeclareType = Table.TransformColumnTypes(Source,{{"File Name", type text}}),

    Check = Table.FuzzyNestedJoin(
        DeclareType, {"File Name"},
        DeclareType, {"File Name"},
        "Table",
        JoinKind.LeftOuter,
        [IgnoreCase=true, IgnoreSpace=true, Threshold=threshold]),
    IsDuplicate = Table.AddColumn(
        Check,
        "IsDuplicate",
        each Table.RowCount( [Table] ) > 1,
        Logical.Type),
    Similar = Table.AddColumn(
        IsDuplicate,
        "Similar",
        each Text.Combine( List.RemoveItems( [Table][File Name], {[File Name]} ), ", " ),
        type text),
    RemoveJoin = Table.RemoveColumns(Similar,{"Table"})
in
    RemoveJoin