Disabling Download Manager notifications

I have a Pixel 3 XL with Android P, and for the last 3 days, my phone started vibrating almost every hour, at exactly hh:10m, but without showing any notifications. After much time, I found some sites indicating how to find the origin of the notification: adding a Settings widget to my Home screen, with a Notification log (otherwise I couldn't find the entire log anywhere else). This revealed the cause is Download Manager, informing me at 3:10 AM that I downloaded a file 3 days ago. Now, I don't remember if I tried uninstalling it from the phone, but the fact is that there is **no** such app in the Settings -> Apps & notifications menu, so I cannot change its notification settings. I tried going to the Files app (as some sites mentioned), which states "Notifications: on", but when I select it, the Categories part is empty, so there is nothing to disable. So, **which app is actually emitting the Download Manager notifications, and how can I disable them?**