Category older posts button always shows 404 error

I connected a post category to a menu, so when I click that menu, the posts in the category are displayed.

Even though my category has 41 posts, always I clicked the ‘<-older posts’ button, it returns 404 error. For example, if I set 5 posts to be displayed, only recent 5 posts are displayed and it returns 404 errors when I clicked the ‘<- older posts’ button. If I set 1 post, I cannot see the second recentest post. It is very weird. ??

I cannot find a solution for this problem. Is there any possible solution or hint?

Thanks, in advance.

Image links for helping you to understand. How can I upload images in this forum anyway? These links are from Stackoverflow. (I uploaded this question in stackoverflow too)
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