i've tried on a few systems but i got the same issue. i could not manage to install it. im using this page:

https://www.zabbix.com/download?zabbix=4.0&os_distribution=rhel&os_version=6&db=PostgreSQL

Steps to reproduce:

1. try to install zabbix 4.0 on rhel 7.5 from rpm repository.

Result:
Error: Package: zabbix-server-pgsql-4.0.0-2.el6.x86_64 (zabbix)
Requires: libpcre.so.0()(64bit)
Error: Package: zabbix-server-pgsql-4.0.0-2.el6.x86_64 (zabbix)
Requires: libnetsnmp.so.20()(64bit)
Error: Package: zabbix-agent-4.0.0-2.el6.x86_64 (zabbix)
Requires: libpcre.so.0()(64bit)
Error: Package: iksemel-1.4-2.el6.x86_64 (zabbix-non-supported)
Requires: libgnutls.so.26(GNUTLS_1_4)(64bit)
Error: Package: iksemel-1.4-2.el6.x86_64 (zabbix-non-supported)
Requires: libgnutls.so.26()(64bit)
Error: Package: zabbix-server-pgsql-4.0.0-2.el6.x86_64 (zabbix)
Requires: libevent-1.4.so.2()(64bit)

Expected:

1. successed installation