DAX's PATH function equivalent Custom Column in Power Query

I wrote one that could do ~100,000 rows in ~20 seconds. Appends a column "PATH" to a table. Inspired by this BIAccountant post: https://www.thebiccountant.com/2021/02/10/guest-post-using-list-accumulate-for-input-output-genealogy/, but modified to be recursive.

A record at the top of the hierarchy should have a null in the Parent field. There is no loop protection, so you don't want any records to be their own parents, their own grandparents, etc.

Note that you only invoke the function once on the table as whole, not row-by-row. Add a step along the lines of:

= fnAddPath(#"Previous Step", "ParentID Column Name", "SelfID Column Name")

(Self_Referential_Table as table,  Parent_Column_Name as text,  Self_Column_Name as text) =>
let
    #"Renamed Columns" = Table.RenameColumns(Self_Referential_Table, {{Self_Column_Name, "0"}, {Parent_Column_Name, "1"}}),
    Buffered = Table.Buffer(Table.SelectColumns(
            Table.RenameColumns(Self_Referential_Table,{{Self_Column_Name, "Child"},{Parent_Column_Name, "Parent"}}),{"Child", "Parent"}))
in
    let
        GetParents = (state as table, currentLevelFromLeaf as number) =>
        let
            NextParents = Table.ExpandTableColumn(
                                Table.NestedJoin(state, {Text.From(currentLevelFromLeaf)},
                                Buffered, {"Child"}, "NextLevel", JoinKind.LeftOuter),
                            "NextLevel", {"Parent"}, {Text.From(currentLevelFromLeaf + 1)}),
            result = if List.NonNullCount(Table.Column(NextParents,Text.From(currentLevelFromLeaf + 1))) = 0 then
                [resultTable = NextParents, maxHeight = currentLevelFromLeaf]
            else
                @GetParents(NextParents, currentLevelFromLeaf + 1)
        in
            result,

        //Reformat the Output
        ResultOutput = GetParents(#"Renamed Columns", 1),
        ListOfLevels = List.Transform(List.Numbers(Record.Field(ResultOutput, "maxHeight") + 1,Record.Field(ResultOutput, "maxHeight") + 2, -1), each Number.ToText(_)),
        OutputTable = Table.AddColumn(Record.Field(ResultOutput, "resultTable"), "PATH", 
            each Text.Combine(List.Transform(ListOfLevels, (x) => Record.Field(_, x)), "|")),
        OutputTable2 = Table.RemoveColumns(Table.RenameColumns(
            OutputTable, {{"0", Self_Column_Name}, {"1", Parent_Column_Name}}),
            List.RemoveMatchingItems(ListOfLevels,{"0","1"}))
    in
        OutputTable2

Probably the final Reformatting could be done more cleverly and in fewer lines of code.