In a self-hosted WordPress, comments section can be disabled per post without using a third-party plugin. The following guide below will show you how to do it.
Disable Comments on a WordPress Post
First, on your WordPress dashboard, go to Posts > All Posts then search the article you wish to disable comments.
Click the post title to edit it.
Click Screen Options below your profile picture and display name at the top-right hand corner of the page. Put a check in Discussion box as what you can see in the screenshot above. Click the Screen Options again to hide the options.
Now, scroll down. Find Discussion section. Uncheck ‘Allow Comments’ or include ‘Allow trackbacks and pingbacks on this page’
Do not forget to update the post to apply the change.
Open the post URL in a new tab and see the comment section. It should now be gone.