What is the meaning of the word "bi-haqq" (rightfully/in truth) in the interpretation of "La ilaha illa Allah" (There is no god but Allah) as "There is no god rightfully/in truth except Allah"? And is the belief that the meaning of the Shahada is "No one should be worshipped except Allah" considered correct?

Leave off the whispers and pay them no mind, for you are a Muslim who knows the meaning of the two testimonies (Shahadatayn) and that it is impermissible to worship anyone other than Allah the Almighty. The worship of anything besides Him is false. No matter how much Satan whispers to you that you do not know these meanings, do not give his whispers any attention. Rather, cast them away from you and ward them off, and do not indulge in them, for this is the most effective cure.