https://justfreethemes.com/hypermarket/
https://justfreethemes.com/sshop/
https://justfreethemes.com/savile-row/
https://wordpress.org/themes/ecommerce-gem/
https://wordpress.org/themes/best-ecommerce/
https://wordpress.org/themes/multipurpose-ecommerce/
https://wordpress.org/themes/ultimate-ecommerce-shop/
https://wordpress.org/themes/shuttle-gominimal/
https://wordpress.org/themes/responsive-mash/
You can also search the WordPress repository for “Bootstrap 4” themes (Repo Search).