Create a UICollectionView with a plain header and grouped content (like Apple Health)

ViewController.swift

class ViewController: UIViewController {

	private lazy var collectionView = UICollectionView(frame: .zero, collectionViewLayout: createLayout())
	private var dataSource: UICollectionViewDiffableDataSource<Section, Item>!

	override func viewDidLoad() {
		super.viewDidLoad()
		configure()
		updateUI()
	}

	// MARK: CollectionView
	func configure() {
		collectionView.register(ExampleRow.self, forCellWithReuseIdentifier: "example")
		self.view.addSubview(collectionView)

		collectionView.translatesAutoresizingMaskIntoConstraints = false
		NSLayoutConstraint.activate([
			collectionView.topAnchor.constraint(equalTo: self.view.topAnchor),
			collectionView.leadingAnchor.constraint(equalTo: self.view.leadingAnchor),
			collectionView.trailingAnchor.constraint(equalTo: self.view.trailingAnchor),
			collectionView.bottomAnchor.constraint(equalTo: self.view.bottomAnchor),
		])
		configureDataSource()
	}

	func createLayout() -> UICollectionViewCompositionalLayout {
		return UICollectionViewCompositionalLayout { sectionIndex, layoutEnvironment in
			let configuration = UICollectionLayoutListConfiguration(appearance: Section(rawValue: sectionIndex) == .header ? .plain : .insetGrouped)
			return NSCollectionLayoutSection.list(using: configuration, layoutEnvironment: layoutEnvironment)
		}
	}

	// MARK: Data Source

	enum Section: Int {
		case header
		case content
	}
	enum Item: Hashable {
		case row(Int)
	}

	func configureDataSource() {
		self.dataSource = UICollectionViewDiffableDataSource(collectionView: self.collectionView, cellProvider: { collectionView, indexPath, itemIdentifier in
			let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "example", for: indexPath) as! ExampleRow
			return cell
		})
	}

	func updateUI() {
		var snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
		snapshot.appendSections([.header])
		snapshot.appendItems([.row(1), .row(2), .row(3)], toSection: .header)
		snapshot.appendSections([.content])
		snapshot.appendItems([.row(4), .row(5), .row(6)], toSection: .content)
		self.dataSource.apply(snapshot)
	}

	class ExampleRow: UICollectionViewListCell {

		override init(frame: CGRect) {
			super.init(frame: frame)
			let label = UILabel()
			label.text = "Hello"
			label.translatesAutoresizingMaskIntoConstraints = false
			self.contentView.addSubview(label)
			NSLayoutConstraint.activate([
				label.centerXAnchor.constraint(equalTo: self.contentView.centerXAnchor),
				label.centerYAnchor.constraint(equalTo: self.contentView.centerYAnchor),
			])
		}
		
		required init?(coder: NSCoder) {
			fatalError("init(coder:) has not been implemented")
		}
		
	}
}