OrangeHRM doesn't currently have a setting that blocks an employee from cancelling a leave request that's still pending approval, even if the leave dates are in the past. Any pending request can be cancelled up until it's approved or rejected.

If you want visibility into cancellations rather than blocking them outright, add the line manager as an additional recipient on the leave cancellation notification, or review cancelled requests through the Leave List.

Note: This is a reporting/notification workaround, not a system restriction — there's currently no way to prevent the cancellation itself.