Serving coffee under pressure from CO2 could potentially lead to carbonated coffee. Some of the factors involved in the coffee becoming carbonated will be:
The temperature of the beverage
The pressure of the CO2
The duration/time that the beverage is under CO2 pressure
For serving coffee, always suggest converting to a Nitrogen system. Nitrogen gas has larger molecules and is less likely to be absorbed by the liquid. Generally, the coffee shops that we work with run through their cold brew coffee kegs daily, so the beverage is rarely under pressure for more than 8 hours.
CO2 can be used at very low pressure to serve for short periods, but leaving the keg under CO2 pressure for any extended period of time could cause the coffee to become carbonated.