You should probably know about... (17 Part Series)
As a natural evolution with both SPA-sites and JAM stack sites, headless CMS has started to gain traction. A headless CMS is basically WordPress without the UI. You use an API to access the pages and the UI to create/edit pages can be external. There's two main kinds of headless CMSs, API-based or Git-based, and this distinction mostly has with how you store the documents in your CMS. Either you use some kind of API or you just store the documents in a Git repository.