I wonder whether it is really secure to store the Two Factor Authentication seed code (e.g. the secret key for TOTP) within a password manager together with the user and password for the service.

If someone gets access to the decrypted password database (e.g. while the password manager is unlocked or by brute forcing the master password), the attacker also has access to the TOTP token which makes Two Factor Authentication pretty useless.

In my eyes, storing the Two Factor Authentication code in the password manager is everything beyond secure.