Currently when you create a modern page, you create a page with 'SitePages' content type and as creator or designer of page you can arrange sections on page as you want. Question is can we define named layouts for SitePages like we do with PageLayouts for modern page so when user select that named SitePage template, new page is created in that templated layout and user can change the layout if he wants once created?
The only option to create similar pages at the moment (without using custom code) is to copy an existing page. It's far from being ideal, but you can create a "template page" and then copy it every time a new page is required.
Again, this is clearly not an alternative to page layouts, but maybe it could work for your requirements