I'm not sure why people are getting offended. Advice has been given politely and the advice is correct.
I'll summarise the options for passwords/auth: If the "disable password auth" setting for SSH is enabled via LE settings or by adding extra config to the sshd.conf file (which is what LE settings does) the SSH daemon is still running and you can still SSH to the box and will receive a password prompt but the default root/libreelec credentials will not be accepted. To use key authentication instead of passwords you need to copy your public key to the box before disabling password auth so that private/public key auth can work (same as any other Linux distro). If you simply want to secure the box so that password login can't be used you can turn SSH off in LE settings and nobody can login. If you need access for something turn SSH back on again.
Anything else is not possible .. so choose and calm down.