Simple tidyr like complete function in Power Query M

Complete2.m

// Paste this into new blank query called Complete2

(table as table, columnName1 as text, columnName2 as text) as table =>
let
    allColumnNames = Table.ColumnNames(table),
    otherColumnNames = List.RemoveMatchingItems(allColumnNames, {columnName1, columnName2}),
    crossed = Crossing2(table, columnName1, columnName2),
    joined = Table.NestedJoin(crossed, {columnName1, columnName2}, table, {columnName1, columnName2}, "crossing", JoinKind.FullOuter),
    expanded = Table.ExpandTableColumn(joined, "crossing", otherColumnNames),
    reordered = Table.ReorderColumns(expanded, allColumnNames)
in
    reordered

Crossing2.m

// Paste this into new blank query called Crossing2

(table as table, columnName1 as text, columnName2 as text) as table =>
let
    // Select the distinct values of each column as its own table
    // Add a helper column to each table called "__cross" that has a constant value of 1
    column1 = Table.AddColumn(Table.Distinct(Table.SelectColumns(table, {columnName1})), "__cross", each 1),
    column2 = Table.AddColumn(Table.Distinct(Table.SelectColumns(table, {columnName2})), "__cross", each 1),

    // Perform a cross join on both tables using the helper column
    joined = Table.NestedJoin(column1, {"__cross"}, column2, {"__cross"}, "column2", JoinKind.Inner),
    expanded = Table.ExpandTableColumn(joined, "column2", {columnName2}, {columnName2}),

    // Clean up by removing the helper column from the result
    cleaned = Table.RemoveColumns(expanded, {"__cross"})
in
    cleaned