The issue is also happening on latest iOS 14 beta 5.
the below workaround solution works for me, presenting a invisible view controller first and then presenting activity vc.
so, it activity vc won't harm required vc, invisible vc will get dismissed instead.
let vc = UIViewController()
vc.modalPresentationStyle = .overCurrentContext
vc.view.backgroundColor = .clear
avc.completionWithItemsHandler = { [weak vc] (_, _, _, _) in
if let pvc = vc?.presentingViewController {
		 pvc.dismiss(animated: true, completion: nil)
} else {
			vc?.dismiss(animated: false, completion: nil)
}
}
present(vc, animated: false) { [weak vc] in vc?.present(avc, animated: true) }