Create ARR__c on the Opportunity Line ltem object, matching the field configuration of ARR__c on SBQQ__QuoteLine__c

Create a cross-object formula field on the Opportunity Line Item to reference ARR__c data SBQQ__Quoteline__c

Create ARR__c on the Opportunity Line Item object, and create a flow to copy the value from ARR__c on SBQQ__QuotelLine__c

Create ARR__c on the Opportunity Line Item object, and create a price rule to copy the value from ARR__c on SBQQ__QuoteLine__c to ARR__c on Opportunity Product