change the featured image size

hello, how do I set the featured image in posts so that it doesn’t crop the images and just uses the same image size as the source. for example all my featured images are designed to be 344W x 373H but when I set them as the featured image they get chopped and are displaying as 289W x 270H in my posts

I installed the simple-image-sizes plugin and tried adjusting the featured image settings but it did not change anything on the post

thank you