Historic question.

Note that Apple now have UICollectionViewCompositionalLayout, which is trivial to use.

(Essentially just set fractionalWidth to 1.)

All previous apple systems for sizing collection views were garbage, and they finally fixed it with UICollectionViewCompositionalLayout.

In a vertical UICollectionView ,

Is it possible to have full-width cells, but, allow the dynamic height to be controlled by autolayout?

This strikes me as perhaps the "most important question in iOS with no really good answer."

When using UICollectionViewCompositionalLayout make sure you set both itemSize and groupSize height to .estimated:

My problem was that I was using .fractional(1) for item height and .estimated(44) for group and it didn't work.

extension TasksController {
    static func createLayout() -> UICollectionViewLayout {
        UICollectionViewCompositionalLayout { (sectionIndex: Int, _ NSCollectionLayoutEnvironment) -> NSCollectionLayoutSection? in
            let height: CGFloat = 44

            let itemSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1.0), heightDimension: .estimated(height))
            let item = NSCollectionLayoutItem(layoutSize: itemSize)


            let groupSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1.0), heightDimension: .estimated(height))
            let group = NSCollectionLayoutGroup.horizontal(layoutSize: groupSize, subitem: item, count: columns)

            let section = NSCollectionLayoutSection(group: group)
            return section
        }
    }
}