FlickrSearch is an iOS 15 sample app. It is a simple TabBar app that displays two UICollectionViews. Both of which use DiffableDataSources. The Search view uses a UISearchController to find photos on Flickr (you need to get a free Flickr api key to use). The DiffableDataSource is used to organize and group searches into sections where they are laid out using UICollectionViewCompositionalLayout for a design nicer than a simple flow. Async / await is used for the network download. Views are laid out using NSLayoutContraints programatically. The Recents tab displays the most recent photos from Flickr in a simple flow layout. Selecting a photo in either view displays it in it's own controller which lets you zoom in and out of the photo. Navigation is done using a simple instance of the Coordinator pattern (no, not the SwiftUI one).
FlickrSearch is licensed under the Unlicense. See the LICENSE file for more information, but basically this is sample code and you can do whatever you want with it.