How much impact does the theme have? For example. The product description for the theme named “ULTRA” is a slide out style. Is the full description still easily read?
Hello and sorry for the late reply, I never noticed the question.
The theme itself will have an effect, but as there will be so many themes, it’s hard to tell you what you need to do.
So the first step I recommend you take is to check the landing page requirements, which detail what you need: About landing page requirements - Google Merchant Center Help