Seems like this has been requested since at least 2016.
In 2021 Instructure replied, saying other things were a priority on the short term, such as having search, sorting and filtering options in the Pages index (since then, they've implemented sorting).
There is a Chrome extension to add folders, and perhaps a tampermonkey script for that too (though I couldn't find it now), but those require every user to install them (and to use a Chromium based browser), so it might not be convenient (or in case of the extension, FERPA compliant?).
But for your use case, why not organize the pages within modules, or pages themselves? It is more work when making new pages, but it also gives more flexibility than a folder structure would give.
Also, "older pages" that are not currently being used can be unpublished, if you want to hide them from students.