Can I stop the 3D model spinning or hide the AR button for one product?

Yes, both are set per model.

1. Go to Plugins → 3D Customizer, open the Models tab and click Edit on the product.
2. Untick Auto-rotate to stop the slow spin when nobody is touching the model. Shoppers can still turn it by dragging.
3. Untick AR enabled to hide the "view in your space" AR option for that product.
4. Click Update model.

The Features column on the Models list shows AR and Auto-rotate badges, so you can see at a glance which products use them.

While you are there, add a Poster image. It is shown while the model loads, instead of a plain "Loading 3D model…" message.