Hello Gopikrishna ,

Please try with the below trigger and let me know further :

trigger OpportunityLineItemTrigger on OpportunityLineItem (after update) {
    // Collect the Opportunity Ids related to the updated Opportunity Line Items
    Set<Id> opportunityIds = new Set<Id>();
    for (OpportunityLineItem oli : Trigger.new) {
        opportunityIds.add(oli.OpportunityId);
    }
    
    // Query the related Opportunities and check the status of their Opportunity Line Items
    List<Opportunity> opportunitiesToUpdate = new List<Opportunity>([
        SELECT Id, (SELECT Id, Status FROM OpportunityLineItems) 
        FROM Opportunity 
        WHERE Id IN :opportunityIds
    ]);
    
    // Update the Opportunities if all Opportunity Line Items are closed
    List<Opportunity> opportunitiesToUpdateStatus = new List<Opportunity>();
    for (Opportunity opp : opportunitiesToUpdate) {
        Boolean allLineItemsClosed = true;
        for (OpportunityLineItem oli : opp.OpportunityLineItems) {
            if (oli.Status != 'Closed') {
                allLineItemsClosed = false;
                break;
            }
        }
        if (allLineItemsClosed) {
            opp.StageName = 'Closed';
            opportunitiesToUpdateStatus.add(opp);
        }
    }
    
    // Perform the update on the Opportunities with closed Opportunity Line Items
    if (!opportunitiesToUpdateStatus.isEmpty()) {
        update opportunitiesToUpdateStatus;
    }
}

If this helps , please mark this as best answer.
Thank you.