Heat a water bath with a sous vide cooker to 55°C (131°F) for medium-rare. Pat the venison dry, season with salt and pepper, and seal in a bag with the ginger, using a vacuum sealer or the water-displacement method.
Lower the bag into the bath and cook for 1 1/2 to 2 hours, until the center reaches the bath temperature. For safety, cook for at least 1 1/2 hours.
About 70 minutes before the venison is done, combine the rice, broth, and ginger slices in a large pot and bring to a boil. Reduce to a gentle simmer with the lid slightly ajar.
Simmer for 60 minutes, stirring from the bottom every 8 to 10 minutes, until the grains have burst and the congee looks creamy and coats the back of a spoon. Add hot water if it thickens too much. Remove the ginger, then season with salt and white pepper.
Remove the venison from the bag and pat it very dry with paper towels. Heat the oil in a cast-iron skillet over high heat until it just begins to smoke.
Sear the venison for about 1 minute per side, until a deep brown crust forms, with a loud sizzle. Transfer to a cutting board and rest for 3 minutes.
Slice the venison across the grain into thin slices, about 1/4 inch (6mm) thick. The center should look evenly rosy from edge to edge.
Ladle the hot congee into bowls and fan the slices over the top. Finish with scallions, ginger matchsticks, a drizzle of soy sauce and sesame oil, and cilantro.