You can access and import pre-made templates directly from the WordPress block editor when creating or editing any post type.
Clicking on the lego icon at the top right of the editor will toggle the visibility of the pre-made template import panel. Within this tab, you can easily find a new layout to insert by scrolling through the list of pre-made layout packs.
Once you find and select a template or layout to import, you will be able to see a live example of it by clicking on the Preview link over the template screenshot. When you are ready to use the template or layout, simply click the Insert button to deploy the pre-made template on your page.
Inserting a pre-made template to a page is not a one-time thing, and you can access to these layouts at any time within the WordPress block editor interface for new or existing pages.