Wix supports Sketchfab iframes in custom HTML code blocks.
Go to Add → More and drag the HTML Code block into your site.
Place and resize the block to meet your needs, then click Enter Code (or the settings cog).
Copy and past the Sketchfab embed code.
<div>wrapping the Sketchfab iframe for it to work on Wix.
And your embed is ready to go!