Naming difference:

Package names:

• zabbix-server-pgsql
• zabbix-web-pgsql
• zabbix-proxy-pgsql

SQL scripts path:

• /usr/share/zabbix-sql-scripts/postgresql

Frontend database type definition parameter:

$DB['TYPE']             = 'POSTGRESQL';

The naming should be unified - use a well-known abbreviation (pgsql) or full software name (postgresql) everywhere, but not both namings in different places.
It is confusing and requires a lot of workarounds in automation tasks.