@Rexleonis, I just found a link to “Passiv” from IBKR website which sounds like it could do the trick. I am not clear if it would be necessary to take the premium plan for USD 99/year. I will try to check it out later
Does your German account have any fees? I have an online broker account in UK that offers commission free regular investing on day x of each month but with fixed account fee GBP 9.99 per month