The MyWage salary advance is not a loan, but a pre-financing of a part of your already earned salary. There is no interest and currently no fees (as of January 2025).
Using the MyWage advance has no impact on your creditworthiness or your SCHUFA score.
A loan, on the other hand, is a borrowed sum of money that you have to repay with interest over a longer period of time. Loan applications and taking out a loan can have an impact on your creditworthiness and your SCHUFA score, as these transactions are recorded by SCHUFA.