$ doas pkg_add postgresql-server

$ doas su - _postgresql

$ # 下記 --locale の指定は必要に応じて行います
$ # スーパーユーザーすなわち下記 "postgres" のパスワードを聞かれます
$ initdb -D /var/postgresql/data -U postgres \
      -W -A scram-sha-256 -E UTF-8 --locale=xx_XX.UTF-8

$ exit

$ doas rcctl enable postgresql
$ doas rcctl start postgresql

$ doas pkg_add postgresql-server

quirks-6.42 signed on 2023-01-13T18:22:41Z
postgresql-server-14.5:postgresql-client-14.5: ok
useradd: Warning: home directory `/var/postgresql' doesn't exist, and -m was not specified
postgresql-server-14.5: ok
The following new rcscripts were installed: /etc/rc.d/postgresql
See rcctl(8) for details.
New and changed readme(s):
    /usr/local/share/doc/pkg-readmes/postgresql-server

$ doas su - _postgresql

$ initdb -D /var/postgresql/data -U postgres \
      -W -A scram-sha-256 -E UTF-8 --locale=xx_XX.UTF-8

The files belonging to this database system will be owned by user "_postgresql".
This user must also own the server process.

The database cluster will be initialized with locale "ja_JP.UTF-8".
initdb: could not find suitable text search configuration for locale "ja_JP.UTF-8"
The default text search configuration will be set to "simple".

Data page checksums are disabled.

Enter new superuser password: 
Enter it again: 

creating directory /var/postgresql/data ... ok
creating subdirectories ... ok
selecting dynamic shared memory implementation ... posix
selecting default max_connections ... 20
selecting default shared_buffers ... 128MB
selecting default time zone ... Asia/Tokyo
creating configuration files ... ok
running bootstrap script ... ok
performing post-bootstrap initialization ... ok
syncing data to disk ... ok

Success. You can now start the database server using:

    pg_ctl -D /var/postgresql/data -l logfile start

$ exit

$ doas rcctl enable postgresql
postgresql(ok)

$ doas rcctl start postgresql
postgresql(ok)

$ psql -U postgres
Password for user postgres:

psql (14.5)
Type "help" for help.

postgres=#