I have two use cases that overlap, thus the two requests:
I would like a way to hide purchased items from showing up in my Library in the course of normal use (as well as a way to look at the Hidden items), preferably without removing indications that I have already purchased them from their pages, just in case.
And
I would like a way to sort games into mutually-exclusive groups, so that I can tell if I have missed anything, or possibly acquired new items that fit one of my categories. In the desktop app, this could be shown on the Library page, along with All Items and Installed Items. Like shelves in a Library, or the way categories are set up on Steam, I would like to be able to "sort down" my uncategorized games, so that I am not presented with an overwhelmingly long list.
Yes, the reason I want both of these is because of the Racial Justice and Equality bundle. While the overall pile hasn't been dumped into my Library, just the number I am trying is enough to get overwhelming, and it is guaranteed that everyone will end up downloading at least a few that are completely not to their taste without knowing it until afterwards, or just a whole lot of one kind of thing they do like, enough to overwhelm the other things in their collection. These two features would help with this, and any other situation of users with large collections.