Convert table with year rows and month columns to table with date column

If that's not what you want, spend another hour to publish a copyable table

let
    Origine = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("TZNLksMgDAXv4nUW1geQzpLK/a8xpgWDN6qUX/ml3Yjv99Jb7utzyc2s38o0pjMbszMHM5g5p/KuPu/+PhQKhY3CQWFSxfNmVJEO0khKhJKZqs5UbexCfbE5bEEVz3t/8ThVQYlSMlOFX7vvQhgEBoPKIek8H9AmDHyL6kzVYWvQDtKUXegvb8UG1eB56vIzq2DzvnieGTM1HJrELoQND+LtGAv+F7fLEqmSKqmRGqk96Srs50zL22KDRIqqLEEbTlWnaqaGQxu6CzFmUOFEAj83rrCqDSp82m1UDaqEKggzd2GcfaszXd6KDVfsnmZR4c1h41sch659F+axN+zsGNuobRxj7IOxn9ahzUHVTP3Z2CrU112IvfP/3mBb54hn475YFhWTdz32TdG6EXWy8EixwYlPkzpHvGHS2UlnGx2H7d43RetGvO5C7VudaXlbbJxvztRtpo7zBn+z56b8/gA=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [year = _t, gen = _t, feb = _t, mar = _t, apr = _t, mag = _t, giu = _t, lug = _t, ago = _t, set = _t, ott = _t, nov = _t, dic = _t]),
    #"Modificato tipo" = Table.TransformColumnTypes(Origine,{{"year", Int64.Type}, {"gen", Int64.Type}, {"feb", Int64.Type}, {"mar", Int64.Type}, {"apr", Int64.Type}, {"mag", Int64.Type}, {"giu", Int64.Type}, {"lug", Int64.Type}, {"ago", Int64.Type}, {"set", Int64.Type}, {"ott", Int64.Type}, {"nov", Int64.Type}, {"dic", Int64.Type}}),
    #"Trasformate altre colonne tramite UnPivot" = Table.UnpivotOtherColumns(#"Modificato tipo", {"year"}, "Attributo", "Valore")
in
    #"Trasformate altre colonne tramite UnPivot"

See the working here - Open a blank query - Home - Advanced Editor - Remove everything from there and paste the below code to test (later on when you use the query on your dataset, you will have to change the source appropriately. If you have columns other than these, then delete Changed type step and do a Changed type for complete table from UI again)

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("XZA7DgIxDETvknqL2HFs5xJcYLUFPQiJ+xfkhdBQ7MifyRtrz7No1VqOItqmUpk5mn33w2OqJnUXdl5977IqilirUa5jAQVrByDxw4gnVpfd/399oahUp2mTmI00QoOdJ9FhUHPEOpx5rPMjx9TWUBuoN/IG9pDIhb293s/7g0gMIAjlIc/oZXERRsLhAu37p8TKdX0A", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Year = _t, January = _t, February = _t, March = _t, April = _t, May = _t, June = _t, July = _t, August = _t, September = _t, October = _t, November = _t, December = _t, Total = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Year", type text}, {"January", Int64.Type}, {"February", Int64.Type}, {"March", Int64.Type}, {"April", Int64.Type}, {"May", Int64.Type}, {"June", Int64.Type}, {"July", Int64.Type}, {"August", Int64.Type}, {"September", Int64.Type}, {"October", Int64.Type}, {"November", Int64.Type}, {"December", Int64.Type}, {"Total", Int64.Type}}),
    #"Unpivoted Other Columns" = Table.UnpivotOtherColumns(#"Changed Type", {"Year"}, "Attribute", "Value"),
    #"Filtered Rows" = Table.SelectRows(#"Unpivoted Other Columns", each ([Year] <> "Normal")),
    #"Added Index" = Table.AddIndexColumn(#"Filtered Rows", "Index", 0, 1, Int64.Type),
    #"Added Custom" = Table.AddColumn(#"Added Index", "Date", each try Date.From("1"&[Attribute]&[Year]) otherwise [Year]&"-"&[Attribute]),
    Custom1 = Table.SelectRows(#"Unpivoted Other Columns", each ([Year] = "Normal")),
    #"Merged Queries" = Table.NestedJoin(#"Added Custom", {"Attribute"}, Custom1, {"Attribute"}, "Custom1", JoinKind.LeftOuter),
    #"Expanded Custom1" = Table.ExpandTableColumn(#"Merged Queries", "Custom1", {"Value"}, {"Value.1"}),
    #"Sorted Rows" = Table.Sort(#"Expanded Custom1",{{"Index", Order.Ascending}}),
    #"Removed Columns" = Table.RemoveColumns(#"Sorted Rows",{"Year", "Attribute", "Index"}),
    #"Reordered Columns" = Table.ReorderColumns(#"Removed Columns",{"Date", "Value", "Value.1"}),
    #"Renamed Columns" = Table.RenameColumns(#"Reordered Columns",{{"Value.1", "Normal"}})
in
    #"Renamed Columns"