If you have a large number of resolved tickets in your helpdesk (over a million), you should enable ticket archiving to improve the performance of the agent interface, especially when selecting filters.

Go to Admin > Tickets > Statuses > Archived and select Enabled.

You can set the number of days until a resolved ticket is archived. Archived tickets can still be viewed in the Archived section, but do not show up in other filters. They can be changed back from archived status by agents with the correct permission.