We mean that you needn't to select the category, after create the size guide.
So you can show all size guide list which are created on size guide menu on product admin page.
Please ignore the category option.
Above screenshot will be helpful for you to understand easily.
We changed the backend code, so you can't see the UI changes,
If you have other questions or didn't understand correctly, please let us know again.
Best Regards, C-Themes