Android - Disabling Download Manager notifications

When searching for Download Manager under Settings -> Apps & Notifications you missed listing out the system apps. List them by tapping on the three dots line in the upper right corner and choosing show system apps. Download Manager is a system app and you would find it apps list.

To disable the notifications from that app, tap on that app in the list, then Notifications, and choose an option there that fits your needs.

Just wanted to add an answer for this that I found on Reddit, in case it disappears.

This issue seemed to be fixed for a few people by doing the following: Go to settings -> Apps and Notifications -> see all apps -> three dot menu -> show system. Scroll to Download Manager. Clear cache, clear storage, force stop, disable, enable.

Of course, your download history will be cleared if you do this, but it's up to you to decide if that's worth it :)