Need to implement incremental refresh where DataSource is kusto

Kusto does not emit the native query. It does not mean it is not foldable. Add the step to see if it is folding:

Value.Metadata(PreviousStep)[QueryFolding]

Enable diagnonsis and I think you should be able to find the native kusto query being run.

Not sure if this helps, but this is what I'm using

let 
    FormatArgument = (arg as any) =>
        if arg is date then
            "datetime(" & Date.ToText(arg, "yyyy-MM-dd") & ")"
        else if arg is datetime then
            "datetime(" & DateTime.ToText(arg, "yyyy-MM-dd HH:mm:ss") & ")"
        else if arg is datetimezone then
            "datetime(" & DateTime.ToText(DateTimeZone.RemoveZone(DateTimeZone.ToUtc(arg)), "yyyy-MM-dd HH:mm:ss") & ")"
        else if arg is duration then
            "time(" & Duration.ToText(arg) & ")"
        else if arg = null then
            error "null value passed to function"
        else
            Text.From(arg)
in
    FormatArgument

let 
    KustoFn = (fn as text, args as list, options as nullable record) =>
        Kusto.Contents("yourcluster", "yourdb",
        fn & "(" & Text.Combine(List.Transform(args, #"FormatKustoArgs"), "," ) & ")"
        , options)
in
    KustoFn

Let me know if you see any bugs with using the kusto connector, I do have contributer access to this.