Judging by both the GP's not having been aware of it, and the process described in a sibling comment [1], I suspect the feature has a discoverability problem.
(Does the same feature exist on mobile? How are file attachments represented on mobile?)
The feature exists on mobile, there's a "Related items" section that has a list of file names with a ">" caret next to each one. If you tap on an entry it opens in a new page where you can tap "View document" to see its contents. You can also see when it was created and updated, share it, add tags to it, add it your favorites, and more.
It works perfectly fine, with no missing features. I use it to store private keys and recovery codes, mainly.
(Does the same feature exist on mobile? How are file attachments represented on mobile?)
[1] https://news.ycombinator.com/item?id=30365088