1. Navigate to Lists > Search > Saved Search > New > Item
2. Navigate to Criteria tab > Summary subtab:
Summary Type: Maximum | Field: Formula (Date) | Formula: max(case when {transaction.type}='Sales Order' then {transaction.trandate} end) |Value: is empty
3. Results Tab: Remove all Fields and add below Field
--Name > Summary Type: Group
Save & Run
Notes:
1. This search can also be used for other transaction types such as Purchase Orders, Transfer Orders etc. Just change the formula expression under the Criteria tab with the desired Transaction Type.