When reddit shut down their api every single subreddit on the site went down in comment activity by 75% or more. Comment activity has only been decreasing in the month since then. Post activity has been in decline as well.
Whether this means people stopped using the site entirely or not is up for debate. But in terms of damage to the community on the site it is the single biggest social media failure I have seen on the web since Digg. Even Musk hasn't damaged Twitter as much as the api change has damaged reddit.