Copied from the r/OutOfTheLoop writeup
On May 31, 2023, Reddit announced they were raising the price of access to their API from being free to a level that will kill every third party app on Reddit, from Apollo to Reddit is Fun to Narwhal to BaconReader, potentially even Reddit Enhancement Suite (RES) and old.reddit.com on desktop too. This threatens to make a great many quality-of-life features not seen in the official mobile app permanently inaccessible to users.
This isn't only a problem on the user level: many subreddit moderators depend on tools only available outside the official app to keep their communities on-topic and spam-free. As OOTL regularly hits the front page of reddit, we attract a lot of spammers, trash posts, bots and trolls, and we rely on our automod bot and various other scripts to remove over thirty thousand inappropriate posts from our subreddit.
On June 12th, many subreddits will be going dark to protest this policy. Some will return after 48 hours, others will go away permanently unless the issue is adequately addressed, since many moderators aren't able to put in the work they do with the poor tools available through the official app. This is not something moderators do lightly. We all do what we do because we love Reddit, and many moderators truly believe this change will make it impossible to keep doing what they love.

