Unless I stand corrected
You don't know all the functions of the program apparently.
And it doesn’t allow you to select partitions only .img
The Program lets you select the partition, you're probably just used to using the program's "write" function, where you choose an image and the partition you want to write the image to.
But, it has a "Read" button for backing up a recorded image, where you select the partition you want to back up (read the comments above), and in the path you put where you want to save the backup image.
Search a little more on the internet to find more detailed tutorials, even on youtube you should find something.
How can he make a mistake using win32
Selecting a partition that is unrelated to Recalbox is an example of a mistake.