Nested Text.Contains based on "higher" column

For performance reasons, you should try to avoid adressing the whole table on a row-by-row-basis. Instead, join (or group) on those attributes who have equality operators and continue from the partitions basically.

The following code is a mockup and the crucial steps are the last 2 where you merge and then add a special column that returns the desired true or falses:

let
    CorrespondenceTable = let
                                Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45W8srPyFPSUfLMK0ssSSzJzM9TKMlXyK1UcEksS40pNTAwMi9WcMosKslISaxUKEgsKqlUitWJVgJJA7UFlqYWgzSBxXwzs1PJMAqqzTk/N1WhPLMkQwFIAzWG5+enFJfkJ2crxcYCAA==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type text) meta [Serialized.Text = true]) in type table [Name = _t, Subject = _t]),
                                #"Changed Type" = Table.TransformColumnTypes(Source,{{"Name", type text}, {"Subject", type text}})
                            in
                                #"Changed Type",

    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WCs/PTykuyU/OVtJR8srPyANSbo4+wa5KsTqoki6JZak4JX0zs0GSIUGhEDmQ4phSAwMj82IFp8yikoyUxEqFgsSikspDCxAWEascw2oC6lFcEwsA", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type text) meta [Serialized.Text = true]) in type table [Event = _t, Name = _t, Is_Invited = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Event", type text}, {"Name", type text}, {"Is_Invited", type logical}}),
    #"Trimmed Text" = Table.TransformColumns(#"Changed Type",{{"Event", Text.Trim, type text}}),
    #"Merged Queries" = Table.NestedJoin(#"Trimmed Text", {"Name"}, Correspondence, {"Name"}, "Correspondence", JoinKind.LeftOuter),
    #"Added Custom" = Table.AddColumn(#"Merged Queries", "DesiredResult", each List.AnyTrue(List.Transform([Correspondence][Subject], (x) => Text.Contains(x, _[Event]))))
in
    #"Added Custom"