TopN Based on Characters

kaye123 , you can

• write an SQL query with needed data and load it into the Power Query
• you can create a column in Power Query with transformed value converted to a number (2020_01 vs 202001) and use this new column for sorting, etc..

For the second option taking into account your column is text:

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMjIwMog3MFRQitWBckDsWAA=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Column1 = _t]),
    #"Split Column by Delimiter" = Table.SplitColumn(Source, "Column1", Splitter.SplitTextByEachDelimiter({"_"}, QuoteStyle.Csv, false), {"Column1.1", "Column1.2"}),
    #"Added Custom" = Table.AddColumn(#"Split Column by Delimiter", "Custom", each [Column1.1] & Text.End( "0" & [Column1.2], 3 )),
    #"Removed Columns" = Table.RemoveColumns(#"Added Custom",{"Column1.2", "Column1.1"}),
    #"Changed Type" = Table.TransformColumnTypes(#"Removed Columns",{{"Custom", Int64.Type}})
in
    #"Changed Type"