Controlling thumbnail/featured image cropping dimensions

Hi,

Is there any way to control thumbnail/featuredimages so that they all crop to display as square?

At the moment, I am getting this effect:

https://www.foragables.co.uk/portfolio/project-type/seascapes/

but I would like all the images to be cropped to a uniform size.
Is this something I can determine via functions.php?

Many thanks.