To know the steps for how to turn off comments on Facebook post, you should check the steps mentioned below:
Move to the desired post on the profile for which you want to restrict the comments.
Tap the three-dot option on the top-right corner of the post.
Tap to who can comment on your post.
You need to select one of the three options that are listed below: public, friends, and profile and pages you mention.
Follow the given available options and restrict the people from adding comments on your Facebook post.