Whenever I enable the homebrew setting for a spell-casting character, I get a list of spells at each level that have the prefix "SSoS/" - e.g., "SSoS/Caustic Cloud" is listed as a sorcerer cantrip, amongst many others. I'm guessing these are homebrew spells, but they are not in my homebrew collection, and I don't want to see them. How can I make them go away?

You unfortunately cannot. All homebrew in everyone’s collection is automatically shared with everyone else in the same DDB campaigns. So those spells are in the collection of someone else in that campaign, and the only way to get rid of them is to ask that person to remove them from their own collection. It just is what it is, and there’s unfortunately nothing we can do about it.

At the least the creator used a prefix naming scheme, which makes it easier to ignore such homebrews if you're not in the group that's meant to be using it.

Oh, interesting, I didn't know it came from being in a campaign with someone else who has those in their collection. Thanks for the info.