The featured image is a banner shape. If you use an image with a different aspect ratio, it will automatically get cropped into shape of the banner image. To make sure your featured is cropping in the right place on your posts, you can crop the image before uploading, or using the media library image editing tools.
To crop your featured image using the WordPress image editing tool:
- Open featured image
- Click edit image
- Click crop
- Input aspect ratio 1468:710 (or 21:9)
- Select crop area
- Click apply crop
- Click Save edits
- Click set featured image