Yes, the sender needs the recipient's public key. I did not find any service supporting this. Even Proton Mail (https://proton.me/support/password-protected-ema

Yes, the sender needs the recipient's public key. I did not find any service supporting this. Even Proton Mail (https://proton.me/support/password-protected-emails https://proton.me/support/password-protected-emails) writes, "To read the message, they must enter a previously agreed-upon password." Thus, the sender sends cleartext to the email provider, hehe.