When I go to the Reporting icon () and select a custom reporting period that's longer than 90 days, I receive the following error message: "Custom period can span up to 90 days".
How can I show more than 90 days worth of data for my Support account?
Since the Reporting Overview is meant to offer a snapshot of recent performance in your Support account, it does not have the capabilities to include data for a date range longer than 90 days.
If you want to report on a longer timeframe, you will need to create a custom report using Insights.
This article contains a full list of recipes for custom reports you could create with Insights: Zendesk Insights recipes compilation.