Can managers approve leave for their staff?

Yes, managers can approve leaves on behalf of their staff either from the Web Dashboard or the User App.

In Truein Web Dashboard:

Web Dashboard: Leaves > Leave Approvals > Action Column > Click Approve Leave

In Truein User App:

User App: Three Dots > Leave Management > Manage Leaves > Click on Approve/Reject

Or the Managers can go to Pending Actions > Leave Approval