Enumeration

Nmap

PORT     STATE SERVICE    VERSION
21/tcp   open  ftp        vsftpd 3.0.3
22/tcp   open  ssh        OpenSSH 7.9p1 Debian 10+deb10u2 (protocol 2.0)
80/tcp   open  http       Apache httpd 2.4.38 ((Debian))
5437/tcp open  postgresql PostgreSQL DB 11.3 - 11.9

Four services on a Debian 10 (Buster) box. FTP rejects anonymous login, SSH is a dead end without creds, and Apache serves nothing worth fuzzing. The odd one out is PostgreSQL on 5437 — not the default 5432. A database exposed straight to the network, on a port someone deliberately moved, is where the attention goes.