Amazon DocumentDB 5.0 extends instance support to Amazon EC2 t3.medium and r5 instances, in addition to previously supported Amazon EC2 r6g instances. You can now use Amazon DocumentDB 5.0 free trial with t3.medium instance and upto 96 vCPUs and 768 GiB RAM with r5 instances. Please refer to supported instance specifications to learn more.
Source:: Amazon AWS