To efficiently prevent users (except those with the Sales Manager profile) from changing the Opportunity Status to Closed Lost when the lost reason is blank:
Option D: An error condition formula on a validation rule on Opportunity Validation Rule Formula:
AND(
ISPICKVAL(StageName, "Closed Lost"),
ISBLANK(Lost_Reason__c),
$Profile.Name <> "Sales Manager"
)
*
Reference:
"Validation rules verify that the data a user enters in a record meets the standards you specify before the user can save the record."
- Salesforce Help: Validation Rules
* Why Other Options Are Less Efficient:
Option A: An approval process is for approving records and is more complex than necessary.
Option B: A record-triggered flow could work but is more complex than a validation rule for this simple validation.
Option C: An Apex trigger requires writing and maintaining code, which is less efficient than a declarative solution.