Re,
Un début de réponse :
let
Source = Csv.Document(File.Contents("C:\Users\jeane\Downloads\gl.txt"),[Delimiter=" ", Columns=11, Encoding=1252, QuoteStyle=QuoteStyle.None]),
#"Added Custom" = Table.AddColumn(Source, "Custom", each Date.From(Text.From(2000+Number.From(Text.End([Column2],2)))&"-"&Text.Start(Text.End([Column2],4),2)&"-"&Text.Start([Column2],2)),type date)
in
#"Added Custom"
La formule (sans le type de données date) :
=Date.From(Text.From(2000+Number.From(Text.End([Column2],2)))&"-"&Text.Start(Text.End([Column2],4),2)&"-"&Text.Start([Column2],2))