Yes, every euro that is not invested in stocks or real estate is wasted. You should only keep liquidity that you need within 6 months. The rest can be secured with stop loss.
Without major risk, there is 5 to 7% with ETFs. Whoever wants more has to take risks and inform themselves well. I usually get that. But still not more than 10% annually, because there is always a company that completely crashes... (Airberlin, Wirecard, Vapiano, many companies back then on the Neuer Markt...)
Therefore, the mortgage is never paid off early. That would only bring 1.6% return and would be absolute nonsense.