There isn't much left.

First Facebook with their whole meta thing, then Imgur deleting all NSFW content and images uploaded by non-registered members, afterwards Twitter and now Reddit.

Twitch made a big mistake with their new sponsoring rules, but seems like they are reverting / changing it again due to bad community feedback.

Discord had a few changes the community didn't like, but nothing ground breaking yet. But they get more and more greedy and their platform is filled with scams, hackers, bots and sadly many bad people like child predators and content which Discord support does nothing against. They seem not to care.

YouTube, well, I think they might be next actually. More and longer unskipable ads, restricting or demonetizing many videos, bad communication with their creators and less rewards for smaller creators. In addition, they might put high quality resolutions behind their already existing expensive subscription paywall. There isn't any competition which is urgently needed.

UPDATE: Bad news about YouTube continues. Just now, YouTube Ordered ‘Invidious’ Privacy Software to Shut Down in 7 Days.

Which other big social media platforms are left?