My yard is surrounded by trees. Very little gets sunlight; in fact, I joke about having to mow my weeds.
Can St Augustine Grass Survive in the Bristol TN Area?
St Augustine is not reliably hardy that far north. There are other grass types that could work for you, as well as non-grass groundcovers. This article has more information: https://www.gardeningknowhow.com/lawn-care/lgen/growing-grass-shade.htm
Also, here's an article on grass for your part of the country: https://utextension.tennessee.edu/publications/documents/PB1626.pdf