Separate antennas are available optimized for 1090 and 978 (the FlightAware antennas are generally considered very good) - requiring their own cable runs between antenna and SDR dongle.
https://www.amazon.com/1090MHz-ADS-B-Antenna-66cm-26in/dp/B00WZL6WPO
https://www.amazon.com/dp/B07MXPQN7H
There are instructions here on configuring your RPi to accommodate two SDR dongles, one for 1090 and one for 978.
Essentially you need to show dump1090 and dump978 where to go (which dongle) for their respective data.