Hi,
What category slug should I use to get urls like: example.com/category-name or example.com/subcategory-name
I tried some variations and some don't work at all and some give duplicate id's like /category/96/96
If I use {CATEGORY_NAME} I get 404 errors for category pages.
If I use {CATEGORY_NAME}/{CATEGORY_ID} I get the duplicated ID like above.
If I use {CATEGORIES} if works for subcategories but I get 404 errors for category pages.

You probably have conflict with other page, most usually static pages.

LE: I think I found it, it was because I was using {PAGE_SLUG} instead of {PAGE_SLUG}/{PAGE_ID}.
Will test further and see.

I am also facing the same issue...
How can it be corrected?

How does page slug affect categories url?

Use the slug I suggested for static pages or read the other recommendation.

LE: I think I found it, it was because I was using {PAGE_SLUG} instead of {PAGE_SLUG}/{PAGE_ID}.
Will test further and see.

If you want just slug, do it like help/{PAGE_SLUG} so it's not considered as category URL.