How to deal with multiple data types in a column: some rows are tables and others text

Shimonkepha I would create 2 new columns that separate out Table values from text values. Then you can work with the Table values without getting errors. Once you have what you need, you can always recombine the 2 columns into a single column once again. PBIX is attached below signature:

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WckxJSU1R0lFycQxx1DU0MlaK1YlWCkrNzS/DFHbOz83NLClBSJiYmoElUAwxt7BUio0FAA==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [NAME = _t, KEY = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"NAME", type text}, {"KEY", type text}}),
    #"Grouped Rows" = Table.Group(#"Changed Type", {"KEY"}, {{"Table", each _, type table [NAME=nullable text, KEY=nullable text]}}),
    #"Appended Query" = Table.Combine({#"Grouped Rows", #"Table (2)"}),
    #"Added Custom" = Table.AddColumn(#"Appended Query", "Custom", each if Value.Is(Value.FromText([Table]), type text) then [Table] else null),
    #"Added Custom1" = Table.AddColumn(#"Added Custom", "Custom.1", each if Value.Is(Value.FromText([Table]), type text) then null else [Table]),
    #"Expanded Custom.1" = Table.ExpandTableColumn(#"Added Custom1", "Custom.1", {"NAME"}, {"NAME"}),
    #"Added Custom2" = Table.AddColumn(#"Expanded Custom.1", "Custom.1", each if [Custom] = null then [NAME] else [Custom]),
    #"Removed Columns" = Table.RemoveColumns(#"Added Custom2",{"Custom", "NAME"})
in
    #"Removed Columns"