Steps to reproduce:
Install Zabbix 4.0.28 under CentOS 7.
Try to access any graph.

Result:
Graphs do not work.

Expected:
According to:
https://www.zabbix.com/documentation/4.0/manual/installation/requirements
Zabbix 4.0 should work under PHP 5.4.0

$ grep ": array" include/classes/graphdraw/CLineGraphDraw.php
private function getOptimalDateTimeIntervalSpec(int $pref_sub_interval, float $min_sub_interval): array {
private function getDateTimeIntervals(int $start, int $end, DateInterval $interval): array {

Looks like Zabbix 4.0 is using PHP 7 features:
https://www.tutorialspoint.com/php7/php7_returntype_declarations.htm

Please clean PHP code from non supported features.