F4 American immigrant visa, the materials have been submitted (paper), but my mother still wants to transfer the money to the applicant's account, saying that it will be used during the interview?

You have submitted an affidavit of support, and this is the guarantor's certificate. As long as the guarantor has enough funds for your living. It doesn't matter how many applicants there were before. TOEFL is not helpful for this kind of visa. Don't take the initiative to show it unless the immigration officer asks you for it (almost impossible).