Heat oil in a large skillet over medium. Cook onion, stirring often, until translucent and starting to brown around the edges, 5–8 minutes. Stir in paprika; season with salt. Add collard greens a handful at a time, stirring to wilt after each addition before adding more; cook until all greens are wilted but still somewhat firm, about 4 minutes. Stir in vinegar. Taste and add more salt if needed.