Standard Notes uses stronger encryption technology than industry-leading password managers. In most cases, leading password managers use PBKDF2 for key derivation and AES-256 for encryption. Standard Notes uses post-PBKDF2 Argon2 for key derivation and post-AES XChaCha20-Poly1305 for encryption. This means that Standard Notes makes for an excellent place to store passwords, keys, and other secretive credentials.
In addition, two-factor authentication enabled on your account can lead to even higher levels of security than offered by typical password managers.