Okay, seems like I’ve mis-read the function. I’m currently under the curse of 素材詳細画面においてお気に入り登録した装備が表示されない場合がある / Favorited equipment may not display in the material details screen, so none of my favourited equipment would cause my items to be listed as bookmarked.
Also, the function is more of showing you the total needed but only when you’re viewing the Material, which is a far cry from what I was expecting when I first read the announcement post.
Ah, well. Shall continue to rely on third-party websites for item box management until then.