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.
Effectively, doc is totally empty (not the first time so).
There is another property: var excludedActivityTypes: [UIActivity.ActivityType]?
So, would allowsProminentActivity enable activities considered as most usual (prominent) ?
In anycase, that's worth a bug report against documentation as 15.4 is now released, not a beta.
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.