Magento 2 Custom Order Number by Cynoinfotech
https://www.cynoinfotech.com/product/custom-order-number-magento-2-extension/
Magento 2 Custom Order Number Extension by Cynoinfotech allows Magento 2 order numbers to be customized to match your business needs via prefix, suffix, letters, counter or any random numbers. Magento 2 Custom Order Number allows customization of order, invoice, shipment and credit memo numbers with any letters, prefixes, suffixes, variables as per business requirements. For example, a store might have all order numbers in the format ORD-20-06-30-0000003-US.