Starlinks are in low enough orbit to passively decay in less than 5 years, that really can't meaningfully contribute to a Kessler syndrome.

Chinese mega constellations on higher orbits & their spent stages left in space are a bigger issues.

Still in case it got going & made higher orbits unusable, starlink would likely still work just fine on the lower self-cleaning orbits, not to mention using a partial (and hopefully soon full) RLV for replenishment.