It was basically worse than prospecting, due to audience size. Algorithms don't like working with small audiences, and you end up paying more on the CPM side, which results in a higher CPI/CPA in the end - which means retargeting isn't worth it.
Moreover, when you run prospecting for iOS, you're already doing some retargeting by default, since Meta can't have full visibility over the user pool due to iOS privacy limitations.
I recommend testing retargeting if your audience size is big enough, and always trying to target users who already show some kind of intent with your product (tutorial complete, first action, or something that makes it worth paying the extra difference on the CPM).