Postgres array_replace function not existing in version 11, 12

Question

Quite frustrating that array_replace function exists in version 9, but not in 11 or 12. Is there a way to activate this function or something of that sort? Please help

I am running Postgres 11.5, select version() gives me the following

version
------------------------------------------------------------
 PostgreSQL 11.5, compiled by Visual C++ build 1914, 64-bit 

When I list the functions using "\df" array_replace() is NOT one of the few array based functions listed

    List of functions
 Schema |         Name          | Result data type |        Argument data types         | Type
--------+-----------------------+------------------+------------------------------------+------
 public | armor                 | text             | bytea                              | func
 public | armor                 | text             | bytea, text[], text[]              | func
 public | array_append_distinct | anyarray         | anyarray, anyelement               | func
 public | array_distinct        | anyarray         | anyarray                           | func
 public | array_sort            | anyarray         | anyarray                           | func
 public | citext                | citext           | boolean                            | func
 public | citext                | citext           | character                          | func
 public | citext                | citext           | inet                               | func