How to remove empty sidebar on Widgets area

Hi,
after months of development of a client’s website, i just realize that there are thousands of widget area in the website created automatically from post categories, causing the WordPress backend works very slow (15 seconds to load each page) see printscreen https://drive.google.com/file/d/1-_itJfcc1D2-pxSnjCfiocNTtjnPPiYk/view?usp=sharing

How do i remove this? without removing the categories post.
Hope this will speed up the backend a bit.

thank you

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