Update:
Further on down in this thread, someone recommended to look for leftover backups:
This was different from what I was seeing on the admin control panel in terms of backup files:
Previously, I was manually deleting those backups in the control panel, but doing so didn’t free up any space.
I think these “leftover” backups that omarfilip was talking about might have been failed backups of some sort? Anyway, when I looked in that /standalone/backups/default directory, I found two very large files:
Deleting these two files (which I think were unsuccessful backups, since they don’t show up in the admin control panel) actually did free up a bunch of space. We’re now at 73% usage of the 160GB, which should mean that we’re fine for the near future.