We developed an end-to-end encrypted communication protocol for Ethereum users. Users with only Ethereum public key can not implement end-to-end encrypted  communications. We create a new pair of public key and private key bonding with users' Ethereum address. On the other hand, if users trust us and will to import their Ethereum private key to us, we can directly implement the end-to-end encrypted communication without creating a new pair for users. Based on cryptography, we can create public keys on different chains such as Bitcoin/Solana and other Evm-Chains. In this way, we can help the users on Ethereum network to easily communicate with users on other chains. In our dapp he can directly search a Bitcoin address and message to that guy with end-to-end encrypted messages.
It's all the same for other web3 protocols such as Nostr/Lens/Farcaster.  Use the same cryptography method we can create the public key on those protocols with users' private keys on Ethereum. Then they can directly message to the users of Nostr through Dessage with their identities of Ethereum. 