I could be wrong, but to the best of my knowledge public collections are used to help recommend similar games in certain parts of itch.io, not sure which. Your private collections are private either way.
I'm not sure how blocking works on itch.io, I think it's more like muting on other sites, but don't take my word for it. And yes, you can see your game is in some private collections, but you can't see what they're called or anything. Only a count,
