To select the most prominent subject in your composition, you can use the intelligent Select Subject feature.
Powered by Machine Learning models for automatic subject selection, this feature comes in line with Affinity's ambition to use ML for the benefit of faster workflow. Models are installed as pre-trained set and do not use any of your own data for further training. Because the operation works 'on device', none of your data leaves your machine at any time.
The Select Subject feature can be accessed via the top menu's Select entry. It uses a Saliency Machine Learning model to identify the most prominent subject on a layer.
The Select Subject feature does not have any customisable options. However, if you wish to add or subtract from the selection, use Affinity's raster selection tools with an appropriate mode set. You can also refine subject selections, mask, and work on subject selection areas as you normally would when using those tools.