It is not stranding, it is Apple adding features to the three applications that are only available in newer releases of the operating system and thus, require those operating system versions for installation.
You can use your existing hardware until it fails, and at some point, it will, and then you will be looking at newer replacement hardware that should support more current versions of these applications. That may also require some periodic budgeting for new hardware so that when the time arrives, it won't be a mountain to climb financially.
By this time next year, LibreOffice will require macOS Catalina for new updates.