Starlink satellites are in low Earth orbit. They could still cause Kessler syndrome, but aren't as much of a concern as higher orbits.

Here are some quotes regarding this from and Aerospace America article

Regarding satellite proliferation, while there are many more satellites, the company responsible for most of them, SpaceX, places its Starlink satellites in a low orbit so they can naturally deorbit relatively soon — within five or six years, per SpaceX — if they fail.

At around 400 kilometers and into the 500-km realm — home to ISS and the SpaceX Starlink satellites among others — atmospheric drag plays a major role. Dead satellites and debris usually slow and burn up in the atmosphere in just a few years. This natural cleansing process accelerates when the sun becomes more active and solar coronal mass ejections strike Earth and cause the atmosphere to swell. “In those altitudes, we can probably do a lot and we will be forgiven,” Linares says.