Yes you can use the 2TB external drive you have along with the 1TB seagate card to store games but if you want it to run the series x/s version of the game it needs to be on the internal memory or off the 1TB seagate card. I personally have an old 1TB external SSD I still use to store and play old games that aren’t enhanced for series x/s and have no issues. The 1TB seagate card has its own designated slot and doesn’t use the USB port as well.