Instagram is testing a new button that allows users to privately signal they don’t like a comment without revealing it to others. The button, which will be displayed next to the like button in comments on Reels and Feed posts, does not show a dislike count when pressed. However, eventually, disliked comments may be ranked lower in the comments section to create a more friendly experience for users. This test aims to help people better control their Instagram experience and what they’re seeing on the app.
Source: https://www.theverge.com/news/613143/instagram-downrank-comments-button-test