AND(
$Profile.Name <> 'Billing',
$Profile.Name <> 'System Administrator',
OR(
RecordType.Name = 'PO Request',
RecordType.Name = 'Invoice'
),
TEXT(Status__c) <> 'New'
)
Requirement -
USer should be able to edit if
Status = New
OR
Status = Pending Approval AND Prior Status = New
OR
Status = Approved/ Rejected AND PRIOR Status = Pending Approval.