Facebook has implemented a new Aspect Ratio rule. Here's the gist of it:
If you are using an image with a ratio (width:height) between 1.91:1 and 1:1 , your image will be rendered fully.
If the image is higher than 1:1, it will be automatically cropped to 1:1.
If your image is wider than 1.91:1, it will be cropped to 1.91:1.
This is basically what it's going to change:
⚠️This applies only if you're not using your own cropping settings, and if you're not using Dynamic Ads