Vou postar um código aqui de exemplo que pode te ajudar
let Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45Wci1LzSuxUvBz9HVViIiIUIrViVZySSxJtVKoqIAgsJBPfnJiSWZ+HlClf7iHa5ArWDQ0yMdKoby8XC8jUy85PxcshmxgZGQkkoGVlRCEZmCwv6+rRzimkak5OfkQU2MB", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Column1 = _t]), Custom1 = Table.FromRecords(Table.Group(Source,"Column1",{"n",each Record.FromTable(#table({"Name","Value"},List.Transform([Column1],each Splitter.SplitTextByDelimiter(": ")(_))))},0,(x,y)=>Byte.From(Text.StartsWith(y,"Event")))[n]) in Custom1