Aren't regex_*() functions built-in?

Hi,

PostgreSQL 15.4 on x86_64-mageia-linux-gnu, compiled by gcc (Mageia
12.3.0-3.mga9) 12.3.0, 64-bit
(the distro which can't figure out how to provide pgAdmin4)

Aren't all the functions listed in
https://www.postgresql.org/docs/current/functions-string.html
assumed to be included in a base installation?

I'm able to use replace(); but with regex_replace(), I get:
ERROR: function regex_replace(text, unknown, unknown, unknown) does not
exist Hint: No function matches the given name and argument types. You
might need to add explicit type casts.

ncsbe=# \df "replace"
                          List of functions
   Schema   |  Name   | Result data type | Argument data types | Type 
------------+---------+------------------+---------------------+------
 pg_catalog | replace | text             | text, text, text    | func
(1 row)

ncsbe=# \df "regex"
                       List of functions
 Schema | Name | Result data type | Argument data types | Type 
--------+------+------------------+---------------------+------
(0 rows)

There are no regex* functions in /usr/share/postgresql/extension

Thanks,
Pierre