Modern customisable checkout like shoplifty

Feature already exist

You can already customize the checkout page. The theme includes a checkout form editor, an checkout order table editor, and a checkout page layout editor using Elementor or WPBakery (and soon Gutenberg). With these tools, almost any checkout layout can be created, including one similar to Shopify. Therefore, I personally do not think any additional options are needed as everything necessary is already in the theme, and any other alternative options would only confuse people.