Zabbix documentation says: "Clicking on Show in the Graph column displays a bar graph where availability information is displayed in bar format each bar representing a past week of the current year."

This means that availability reports are not available for the past year.
Even if you set the correct filter values by date specifying the past year, the graph will still be for the current year. A huge request to change the work of this function so that we can get a graph for the last year (if we have a history of items).

Than you!)