One key difference between zk-rollups and zkEVMs is that a zk-rollup is focused on scalability, while zkEVM is focused on privacy. A zk-rollup allows for a large number of transactions to be processed off-chain while still maintaining the security and integrity of the Ethereum main chain. On the other hand, zkEVM allows for the execution of smart contracts in a privacy-preserving manner, allowing for the creation of private, confidential transactions on the Ethereum platform.

Both zk-rollup and zkEVM are significant innovations that can help to improve the scalability and privacy of Ethereum. They both have the potential to significantly enhance the capabilities of the Ethereum platform and make it more useful for a wide range of applications.