Create a custom column in Powery Query filtering about another column

Table.Group is useful here. Add the column after you have grouped by month; then re-expand the table:

let

//My source is an Excel table but can be anything
    Source = Excel.CurrentWorkbook(){[Name="Table5"]}[Content],
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"mes", Int64.Type}, {"Categoría", type text}}),

//create list of all the categories
    #"All Categoría" = List.Distinct(#"Changed Type"[Categoría]),

//group by "mes", then add the column in a custom aggregation
    #"Grouped Rows" = Table.Group(#"Changed Type", {"mes"}, {
        {"All Cat present", (t)=>Table.AddColumn(t,"Resultado", 
            each if List.ContainsAll(t[Categoría], #"All Categoría") then t[mes]{0} else null, Int64.Type), 
            type table [mes=nullable number, Categoría=nullable text, Resultado=Int64.Type]}}),

//Re-expand the collapsed table
    #"Expanded All Cat present" = Table.ExpandTableColumn(#"Grouped Rows", "All Cat present", {"Categoría", "Resultado"})
in
    #"Expanded All Cat present"

 Data

Results