In order to create a template that applies on multiple posts or categories you need to use dynamic elements, global blocks & display conditions. This will enable you to work more naturally with the builder by creating pages and templates at the same time. Every page can be a template as well based on the blocks and conditions you have on that page.
We are treating all assets in Brizy Cloud (blog posts, custom posts, categories, pages) as regular pages. In other words, if you want to edit a blog category or blog post, you just go and edit it with Brizy and the same goes with any asset.
When you want to create a template, you just add the dynamic elements in a block, set the block as global, and use the display conditions to put it across your other categories, or posts, or where you need it.