If they can beat the rate of return of holding cash, they would invest into some service or product. Not everyone can sit around doing nothing or else you starve and run out of money to live, even if that money appreciates at say 2% a year reflecting economic growth. Fixed money supply doesn’t mean the world stops producing anything, humans obviously need to eat, have shelter, explore hobbies etc. Entropy also necessitates maintenance and improvement. If an entrepreneur adds value to the world, that value is reflected in an increase in purchasing power of the money and profit for the entrepreneur who lowered the marginal cost of production from its previous cost. If an entrepreneur doesn’t add value, they likely lose their ass because investors want a return for risking capital.