Yes, capital gains tax (Abgeltungsteuer) as well as the solidarity surcharge (Solidaritätszuschlag) and, if applicable, church tax (Kirchensteuer) are automatically withheld from the monthly interest credit and paid to the tax office (Finanzamt).
However, you have the option to set up or adjust a tax exemption order (Freistellungsauftrag) to utilise your saver's lump sum (Sparer-Pauschbetrag) (up to €1,000 for single persons or €2,000 for jointly assessed spouses). In this case, a tax deduction will only occur if your total capital gains at Scalable Capital exceed this amount in the calendar year.
You can conveniently manage the tax exemption order at any time on web under Profile > Taxes > Edit tax exemption and in the app via Profile > Tax exemption > Edit tax exemption.