I have found a few websites that show the cases are compatible with airpods pro and airpods 3. Its much easier to buy the pro cases if they fit the airpods 3
The AirPods 3 include a wireless charging case with MagSafe that's slightly smaller than the AirPods Pro's case, all-new "custom" drivers, spatial audio with dynamic head tracking, "HD voice quality" for FaceTime and an adaptive EQ system to optimize sound quality. Apple's improved the battery life, so they now last up to 6 hours on a single charge instead of 5 at moderate volume levels. They also have the same force sensors in their stems as the AirPods Pro for controlling playback with a pinch. And importantly, they're sweat- and water-resistant with IPX4 certification (splashproof).