The clock widget has the option to set the "Time type" to "host time". Selecting this option makes the "Item" field becomes available and it reads only the specific "system.localtime[local]" item.

By default, this specific item returns the time as a UTC value measured in seconds. When the "local" parameter is added, the item returns the time as a string formatted as "yyyy-mm-dd,hh:mm:ss.nnn,+hh:mm".

I have noticed that not a single Zabbix OOTB template uses the "system.localtime[local]" item key. I could not find a single template that collects the host time as a string format.

This can cause a user to select the native "system.localtime" item without the "local" parameter, resulting in a "No data" value in the clock widget.

For example:

Selecting the "host time" in the clock widget and then the "System local time" item available from the default "Linux by Zabbix agent" template

will result in a "No data" value in the clock widget.

Therefore, the "system.localtime" item in UTC format should be readable by the clock widget. I suggest modifying the clock widget to allow it to read Unixtime items.