Postgres 13

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CREATE TABLE customer (
  id bigint
, name text
);

INSERT INTO customer VALUES(1, 'Adam');

CREATE TABLE

INSERT 0 1

CREATE OR REPLACE FUNCTION pg_temp.dynamic_column_name(_col_name text, OUT return_value text)
  RETURNS text
  LANGUAGE plpgsql AS
$func$
BEGIN
   EXECUTE format('SELECT %I FROM customer WHERE id = 1', _col_name)
   INTO return_value;
END
$func$;

CREATE FUNCTION

SELECT pg_temp.dynamic_column_name('name');

dynamic_column_name

Adam

SELECT 1