There isn't to be shared between the two techs, Groq's hardware is a like a railgun that installs all the weights into the optimal location before firing off an inference. Cerebras computer engineering more convention requiring the same data movement that GPUs struggle with optimizing.
Suspect Groq is complementary/superior to nvidia's GPUs, while it is unclear what Cerebras brings other then maybe some deals with TSMC.
While Apple products may be popular with tech bros and aspiring creative like Martin Luther King, John Lennon or Mahatma Gandhi they only represent a small fraction of computing outside California.
A year ago it wasn't clear if they'd stay competitive but it seems they are.