UIActivityViewController
has an undocumented property introduced in iOS/iPadOS/Mac Catalyst 15.4 called allowsProminentActivity
.
What does it do?
It's related to SharePlay. See What's new in SharePlay from WWDC22.
tl;dw when allowsProminentActivity is true the green Share Play button is shown at the top of the sheet, when false it's shown down below with the other actions.