Support for reusable content in MS365 SharePoint pages

Question

My team manages a knowledge base in SharePoint 365 that is a site pages library (in other words, we're not using a documents library of Word, PowerPoint, PDF, etc. files). Many of the pages we manage have overlapping content, ranging from definitions to entire webparts of identical text or images. When one thing changes, every page requires manual updating in our current structure. I'm heading up a project to rebuild our information architecture.

Unfortunately, I'm unaware of a native feature in SharePoint to apply a content reuse solution as allowed by other platforms (XML-based solutions like DITA, MadCap Flare, etc.). My goal is to allow us to invoke reusable content so that if we need to change 5-10 pages, we can simply update the text in one source location and automatically cascade it to every page that uses it.

For example, if we change a set of steps recur in 15 procedures, or a product title changes that appears on 100 pages, how can I update that in one place and make it automatically apply to every page in our library?