While Do Loop in Power Query M

It looks like you want to tag the first ACTIVATED row. To do this, I'd recommend grouping by [State], taking the min over the date column, filtering [State] = "ACTIVATED", and then merging this back with the step before grouping. Then you can transform the column based on whether or not it's empty.

Here's a sample query you can paste into the Advanced Editor and walk through the steps:

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45Wcnb0c3b18XF1UdJRMtQ31DcyMLQEMZVidVAljfSB0MDIAMQESzo6h3iGOYaAJY31jUGShiAmhqSJvglI0gjEVIqNBQA=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [State = _t, Date = _t, Index = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"State", type text}, {"Date", type date}, {"Index", Int64.Type}}),
    #"Grouped Rows" = Table.Group(#"Changed Type", {"State"}, {{"MinDate", each List.Min([Date]), type nullable date}}),
    #"Filtered Rows" = Table.SelectRows(#"Grouped Rows", each ([State] = "ACTIVATED")),
    #"Merged Queries" = Table.NestedJoin(#"Changed Type", {"State", "Date"}, #"Filtered Rows", {"State", "MinDate"}, "New Column", JoinKind.LeftOuter),
    #"Transformed Column" = Table.TransformColumns(#"Merged Queries", {{"New Column", each not Table.IsEmpty(_), type logical}})
in
    #"Transformed Column"