Hey! NWC (Nostr Wallet Connect) is a protocol designed to enable standardization between a wallet that holds Nostr keys and a client or application that uses Nostr. It does not directly handle private Nostr keys itself. Instead, NWC specifies how clients can securely interact with wallets to perform operations, such as sending or receiving payments, without the need for the client to directly access private keys. So the keys will be in the wallets, whether mobile or browser plugin or pwa.

Hope this clarifies a little bit! Thanks for asking!

- JP