Even though Google has gone though a lot of effort to make Wear OS watches compatible with both Android and iOS devices, they remain second-class citizens on Apple's platform, mostly due to limitations placed on non-system apps by iOS. One of those limitations is finally going away, as long as you have one of Fossil's newest smartwatches.
Fossil just announced that its Gen 5 smartwatches (such as the Caryle and Julianna) can now answer phone calls when paired with an iPhone. Previously, answering calls could only be done with watches paired to Android phones. That makes Fossil's Gen 5 watches the first Wear OS devices ever to support answering calls on iOS.
Sadly, you shouldn't expect iPhone calling to arrive on TicWatches or the ol' reliable Huawei Watch. Fossil says it developed this feature itself, which means it will likely stay exclusive to the company's own watches, as well as watches sold under its sub-brands (Misfit, Kate Spade, Skagen, Michael Kors, and so on).