Insert Table from Execute String Query

I need to insert temp table from execute string query. How can I do ? I'm
trying like that but not working.

CREATE OR REPLACE FUNCTION public.testdyn
(
        x integer
)
RETURNS TABLE
(
        id bigint,
        text character varying(4000)
)
AS $$
        DECLARE mysql TEXT;
BEGIN
        create temp table tmp1
(
id1 bigint,
text character varying(4000)
);
mysql = 'select id, text from TEST';

RETURN QUERY
      EXECUTE mysql INTO tmp1 ;
END;
$$ LANGUAGE plpgsql;