With Facebook looking to boost engagement, one of the key ways it can do so is by ensuring that users see the most engaging, interesting comments on each post, which, ideally, will further prompt them to share their own thoughts. The problem with this is that, sometimes, low-quality comments float to the top - offensive remarks, criticisms, the type of thing that actually discourages further interaction for fear of the same being directed at you.
To address this, earlier this year, Facebook started testing a new up and downvote option for comments, which was designed to give users a way to provide immediate, easy feedback on comment quality, in order to keep on-platform conversations more civil and inviting.

The up/down vote option has appeared and disappeared for various users, but this week, another variation of a similar tool was spotted in the wild.

As you can see, in this new iteration, there's a quick 'Facebook survey' option on comment quality, which helps provide the platform with more feedback into what users like and don't like within discussion threads.
The feedback option, spotted by user Simon Godfrey (and shared by social media expert Matt Navarra), adds another way to help Facebook clean up its comments and prompt more engagement - it's not clear how widespread the option is being tested, nor how prominent it may be. But it underlines, once again, that Facebook is looking at this as a key area fo help boost interaction, which is important, considering various reports have suggested that interaction on the platform is in decline.
How true such reports are is hard to say - the only group that can confirm an engagement decline is Facebook, who don't really have any reason to do so. Definitely, in terms of active users, Facebook has continued to grow, despite a slight dip in Europe and flat performance in North America of late. In theory, that decline could be reflective of a shift away from The Social Network, but there are no definitive stats, only reports based on enclosed data sets.
But the platform's more recent moves do suggest that there are concerns about losing touch. Early in 2018, Facebook rolled out a News Feed update which aimed to put more emphasis on content from friends, and less on Pages, while Facebook has also been pushing Groups, where an increasing amount of user interactions are now taking place.
Comment quality is a small part of the larger picture here, but a relevant one, and it is worth noting the platform's moves to boost engagement and activity.