Since several people asked as follow-up, Kessler Syndrome is where the number of collisions between satellites and/or junk in Earth's orbit continue to increase, even if you don't add more to the system. We're probably already at this point, but the collision rate is very low (so far).
That could change quickly, if there is a collision that releases a large amount of debris close to Starlink's orbital shell, which is by far the densest part of Earth's orbit (and they're adding more every week)