Can't change paginator's PageSize

Are you invoking pagination more than once on the same page?

https://gohugo.io/templates/pagination/#list-paginator-pages

If you call .Paginator or .Paginate multiple times on the same page, you should ensure all the calls are identical. Once either .Paginator or .Paginate is called while generating a page, its result is cached, and any subsequent similar call will reuse the cached result. This means that any such calls which do not match the first one will not behave as written.

If you need further assistance…

Let us see your code

Include a link to the source code repository of your project, because we really need the context of seeing your templates and partials to be able to help you. It is trivial to do a quick git clone on your repo, then run hugo server in your project, to help you out. On the other hand, recreating your code from screenshots, or sort of guessing at it, is not.

If you can’t share your repository for whatever reason, consider creating a dummy repo that you can share, which reproduces the problem you’re experiencing.

See https://discourse.gohugo.io/t/requesting-help/9132.