I agree with the siblings that this isn't true. I've recently finished a big refactor of something entirely back-end with almost no user-visible changes at all

I agree with the siblings that this isn't true. I've recently finished a big refactor of something entirely back-end with almost no user-visible changes at all (except ahem for a bug I wrote), and I could still present progress. The work was the migration of six or so different components: they used to conform to one API, and I moved them to a different API. I found a way to order the changes so that they could be done sequentially rather than big-bang. Bam: a clear progress marker. This kind of progress is pretty common, in my experience. I've already written about defunctionalising an algebra before (https://www.gresearch.co.uk/article/defunctionalisation/ https://www.gresearch.co.uk/article/defunctionalisation/), and that is another example of a task where the work can often divide itself into discrete chunks. You can show your progress to your team, all without the end-user being able to see anything.