Ever since Google introduced WebP image formats, which are a much smaller and lighter image format than jpg or png, Google Merchant Center did not support this image.
You can now use WebP images for the main image_link and additional_image_link.
The primary purpose of WebP images is to speed up your website. Lighter images equal faster websites.
Do You Get Better Ranking In Google Shopping?
There is no evidence showing WebP images have a direct influence on your data feed quality score. However, an indirect ranking result is page speed. IE how long it takes for your product landing page to load. This will impact your ranking, as it is a ranking factor.