In the article Zabbix: how to increase the number of last issues in the dashboard, we already talked about how to change the maximum number of events in the Zabbix panel. However, starting with version 3.4, the dashboard was changed and widgets were added. Recent events have been replaced by the Problem widget. The constant has also changed, which is responsible for the number of problems displayed on the panel. Now this is ZBX_DEFAULT_WIDGET_LINES. It is located in the same defines.inc.php.
Open it with the editor:
sudo nano /usr/share/zabbix/include/defines.inc.php
Find the constant that interests us:
define(ZBX_DEFAULT_WIDGET_LINES , 25);
Change 25 to the value you need, for example, 100:
define( ZBX_DEFAULT_WIDGET_LINES , 100);
Save and close the file.