They are front only. But there are aftermarket matching ones for the rear: https://www.amazon.com/dp/B09N7M3Y3R?psc=1&ref=ppx_yo2_dt_b_product_details
(I ordered and received mine, but have not yet mounted them)

Nansure Tesla Model Y Mud Flaps Rear Splash Guards Mudguard Mudflaps Car Accessories for Model Y 2020 2021 2022, No Need to Drill Holes (Set of 2) https://www.amazon.com/dp/B09N7M3Y3R