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.
You need to remove the "sketchfab-embed-wrapper"
<div> wrapping the Sketchfab iframe for it to work on Wix.
Feel free to experiment with the height and width code to make the viewer fill the Wix element. You can use either pixels, as Sketchfab sets by default, or percentages.
And your embed is ready to go!
Wix "sandboxes" iframes (wraps them in their own iframes), so the fullscreen button may not work as expected. If you want full screen, you can create a dedicated page where the code block fills the entire window.