Despite Huawei's claim, teardown of P20 Pro seems to indicate that all three cameras carry OIS19
Officially, Huawei will only admit that the 8MP camera is equipped with OIS. The manufacturer says that the other two sensors rely on the AI based Neural Processing Unit (NPU) for what it advertises on its website as AI Image Stabilization. But iFixit says that based on its tear-down, it has discovered hardware that would indicate that all three cameras have OIS capabilities (the floating lenses are a solid clue). By the way, to get off the subject just a tad, the NPU can handle things like predictive focus, add different filters like bokeh, and automatically set the camera for 19 different scenes.
Because replacing the screen means going through two layers of adhesive, iFixit gave the Huawei P20 Pro a 4/10 for repairability. Other issues mentioned in the tear down include the glass front and back creating a double hazard and the difficulty in removing the battery (although it can be done). On the positive side, many of the components used in the phone are modular and can be replaced independently.