stack=# select version();
                                                version

--------------------------------------------------------------------------------
------------------------
 PostgreSQL 11.4 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 9.1.1 20190503 (R
ed Hat 9.1.1-1), 64-bit

stack=# CREATE EXTENSION pgcrypto;
ERROR:  could not open extension control file "/usr/pgsql-11/share/extension/pgcrypto.control": No such file or directory

sudo dnf install postgresql-contrib

]$ ls /usr/pgsql-11/share/extension/
plpgsql--1.0.sql  plpgsql.control  plpgsql--unpackaged--1.0.sql