I love this feature. I am curious if you could consider changing or adding an option to scale non-proportionally instead of cropping.
In the current function, cropping will remove part of the original image which could cut out text on the cover that should remain, the effect is amplified the more that the X and Y dimensions differ.
An alternative would be a fill/fit resizing. Yes, it will distort the original image to some degree depending on how disparate the X and Y dimensions are, but I find for album art this is typically the preferable adjustment.
As an example I'll attach this sample album cover original (600x512) and a cropped version from the quick action (512x512) and a resized using the suggestion I'm making (600x600, though 512x512 is going to produce the same image also). You can see how much text could get impacted, and in the resized version the overall image does not appear as "messed up".