Trim the ends off the sprouts and slice into quarters.
Add the cut Brussels sprouts to a large bowl with the oil, vinegar, and salt. Toss well to coat.
Heat air fryer to 390 degrees.
Add your Brussels sprouts to your air fryer basket and air fry for 10 minutes, shaking once halfway through.
Test for doneness after 10 minutes. If Brussels sprouts are not as tender as you’d like, continue cooking and checking every 1 minute.
Notes
If you don't have an air-fryer, follow this recipe for keto brussels sprouts instead. Some balsamic vinegars contain a lot of added sugar. Check for one that is around 3-4 carbs per tablespoon before buying.