I'm trying to reference the product2 name from an opportunity record. However it's giving me this error and not allowing me to save the code.

"Invalid foreign key relationship: Opportunity.opportunitylineitem"

How should I be referencing this field?

global class OpOwnerOldService_Scheduled Implements Schedulable
    {
        global void execute(SchedulableContext sc)
        {
            sendEmailtoOppOwner();
        }

        public void sendEmailtoOppOwner()
        {
            List<Opportunity> listOpportunity = new List<Opportunity>();
            listOpportunity = [SELECT Id, OwnerId FROM Opportunity WHERE Id In (SELECT OpportunityId FROM OpportunityLineItem WHERE Product2.Make_unavailable_for_opps_and_proposals__c = TRUE)];

            for(Opportunity opp : listOpportunity)
            {
               Messaging.SingleEmailMessage mail = new Messaging.SingleEmailMessage();

mail.setTargetObjectId(opp.OwnerId);
mail.setReplyTo('glenn.daly@live.com');
mail.setSenderDisplayName('Salesforce Support');
mail.setSubject('Historic Service attached to current opportunity : '+ opp.  );
mail.setPlainTextBody(opportunity.Id +' has been created.');
mail.setSaveAsActivity(false);
                
Messaging.sendEmail(new Messaging.SingleEmailMessage[] { mail });
            }

            update listOpportunity;
        }
    }