It might be that the automatic HDR, the Deep Fusion, is causing the blur.
Whenever I try to take a picture of the moon at night, the moon will be blurry, but the stars in the background are sharp dots. So the focus is correct for the distance of the stars, which should do for the moon as well.
Looking at the details of the photo with Metapho, I can see that the iPhone 15 Pro Max has been taking the image as a composite of six images and has fused them to bring out the details. This results in an overall exposure time of 3.2 seconds.
The moon is moving relatively fast among the stars. In two hours it is moving once the distance of its own diameter. If the iPhone is trying to track the stars to compensate for the motion of the stars, the Deep Fusion of the moon may result in motion blur because of its motion relative to the stars.
Next time I'll try to take the photos of the Moon as RAW images to avoid Deep Fusion or Night Mode.