Hi, saguaros. Thank you so much for your prompt reply. Question, when you display the category pages on your live website, you don't get an error message? If you don't, then, I wonder why I'm having this issue on my end. Let me show you a couple of screenshots of what I have here:


As you can see, when I try to display the category "Health" on my website, I see a page with this text:
0 - Call to undefined method Joomla\CMS\HTML\HTMLHelper::doSomething()
You may not be able to visit this page because of:
an out-of-date bookmark/favourite
a search engine that has an out-of-date listing for this site
a mistyped address
you have no access to this page
The requested resource was not found.
An error has occurred while processing your request.
Please try one of the following pages: Home Page
If difficulties persist, please contact the website administrator and report the error below..
Call to undefined method Joomla\CMS\HTML\HTMLHelper::doSomething()
Is there a way to know where the problem is coming from? Thanks again, saguaros. I appreciate your help.