We are using Big Commerce to create products which are then imported into WordPress. All of the product imagery is being cropped to 300x300 without regard proportion.
You can see it in action here:
https://bullseyesurplus.com/products/christensen-arms-mesa-308-win-22-in-tungsten-ca10280-h13211/
The actual photo:
https://bullseyesurplus.com/wp-content/uploads/2019/02/Mesa-Gallery_02__69172.1551390214.1280.1280.jpg
The thumbnail is indiscriminately cropping it to a square format.
I’d much rather it resize the image proportionately.