From the 2nd paragraph of the link I posted:

  One of the major differences between AWS Graviton2 instance types and other instance types is their vCPU to physical processor core mapping. Every vCPU on a Graviton2 processor is a physical core. This means there is no Simultaneous Multi-Threading (SMT) and more isolation between vCPUs. By contrast, every vCPU on a 5th generation instance type with Intel processor (such as M5, C5, and R5) is a hyper-thread. This means vCPUs share resources and there is less isolation than in the case of Graviton2.