Reddit was the GOAT, it is hugely helpful for almost every issue you could face and if you pick your subreddits right it's significantly less toxic than other social media. Unfortunately they've been sabotaging themselves lately.
Instagram only to see how close real life friends are doing (I'm a teenager)
I don't like the short videos (YouTube shorts, TikTok etc) but both YouTube and Bilibili are great platforms with lots of great content.