How does zero knowledge protocol like ZkSnark adds privacy in Ethereum?

I am learning about zk tech, esp Snark. I have a basic understanding on how it is applied to Zcash and its conceptual overlap with Tornado cash. I have a few key questions or knowledge gaps about how it can be vastly applied in the Ethereum ecosystem.

1. When people say zk tech can bring privacy to Ethereum, what scale or scope are we taking about? Is it like some specific apps like Dex or Tornado cash like apps where you need to use to archeive that? Or is it something more default? If the latter, like masking transfer or transaction detail (sender, receiver, amount), how is it actually executed?

2. Zcash uses UTXO whole ethereum is account based, is account based more challenging for privacy when applying ZkSnark?