The feature is not available in the newly QB Billpay. You should signup for a free Melio account and it will re-sync your data from the old Billpay powered by Melio. You can combine up to 20 bills.

https://affiliates.meliopayments.com/quickbooks

You can also get $100 cashback to pay the first bill.

https://affiliates.meliopayments.com/cashback