Table Field identifier using a variable

Try this code and see if it works for you...

(fieldname as text, recordProperty as text, delimiter as text) =>
let
/* testing data
    fieldname = "FixVersions",
    recordProperty = "name",
    delimiter = "|",
*/
    /* mocking test data */
    tmp0 = Table.FromRecords({
        [Key= 22, Summary="test1", FixVersions = Table.ToRecords(Table.FromRows(
        {   {1, "DC-24-1", "DC-24-1"},
            {2, "DC-24-2", "DC-24-2"},
            {3, "DC-24-3", "DC-24-3"}
        },  {"id", "name", "value"} ))],
        [Key= 23, Summary="test2", FixVersions = Table.ToRecords(Table.FromRows(
        {   {1, "DC-24-1", "DC-24-1"},
            {2, "DC-24-2", "DC-24-2"},
            {3, "DC-24-3", "DC-24-3"}
        },  {"id", "name", "value"} ))]
    }),
    transformListValues = Table.TransformColumns(tmp0, {{fieldname, each Text.Combine(List.Transform(_, each Record.Field(_, recordProperty)), delimiter)}})
in
    transformListValues