The new quickslots are dedicated to specific purposes, and can't be used for anything else. It's really unfortunate, because extra quickslot wheels could be really useful - SO much more so, if we had a choice what we used them for!

But they can only be used for Emotes, Mementos, Tools, and Allies. The latter three can be filled from Collectibles, from the corresponding sub-menu. Emotes is the most confusing - go to the Help Menu and use the right-most tab, the one that shows what all the emotes are, to fill that one.

It's also confusing in how it's used, because the original quickslot wheel is a two-step process - you have to select which of the quickslot options from the wheel is the active one by holding it down then choosing which is active, then releasing - then to use it, you just tap it.

But the new ones, you don't select an active choice THEN use it - selecting it uses it.