Warm 1 tablespoon of olive oil in a large skillet over medium-high heat until it shimmers.
Add the sausage slices to the hot oil and sauté, turning regularly, until they brown lightly, about 1 to 2 minutes.
Transfer the browned sausage to a plate and set aside.
Add the remaining 1½ tablespoons of oil to the skillet along with the minced garlic, cooking for about 1 minute until fragrant and slightly golden.
Toss in the shredded cabbage, salt, black pepper, and crushed red pepper flakes if using; stir to combine.
Cook the cabbage mixture, stirring now and then, until the cabbage softens but still retains some bite, roughly 10 minutes.
Return the sausage to the skillet and mix it in with the cabbage.
Continue cooking everything together for 3 to 5 minutes more until the sausage is heated through and the cabbage is tender.
Taste the dish and adjust salt as desired before serving.