Cart in woocommerce

Not sure I fully understand what you mean. This is what I see: https://cld.wthms.co/B3lEHe

Yes but some of the photos are not shown as main introduction photo.

If you for example see this product:

https://woidstyle.shop/?product=fototapete-skyline-washington

And you are postive that product has a featured image set on it, and not just gallery images?

If so, then there is a plugin or theme conflict occurring. Follow this guide to find the culprit: https://docs.woocommerce.com/document/woocommerce-self-service-guide/#section-4. You may need to visit the products admin page and re-save after disabling everything.