I'm aware that a DLC-specific search function is being worked on for owned games, it's been a common request for years and as of at least this thread I know it's a current project:
https://steamhost.cn/steamcommunity_com/groups/SteamLabs/discussions/4/1754653387143762580/

As an overlap to this Store experiment and the DLC search function, could said DLC-function be added as a sub-category in the Storefront, perhaps under both/either 'Your Store' and 'Special Sections'? I appreciate said function isn't currently ready and might not be by the time this experiment is ended, but assuming it does I imagine it'll be a popular enough function to warrant its own navigation shortcuts within this new format.