The 3D preview is generated after the model is uploaded, it can take a little while for the 'movie' to become live.
To see the 3D preview 'movie' you need to be in 'public' view mode on the model page (i,e, click Exit Edit Mode if you see that at the top right of the model page)
The 3D preview 'movie' is available by clicking on the box icon below the main model image, e.g.;
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