Reddit, one of the most popular social media sites on the Internet, suffered a major breach. The hackers, whose identities and affiliations are currently unknown, used hacked moderator accounts to post strangely worded pro-Trump messages. Many of the compromised subreddits boast over one million members.
https://www.notebookcheck.net/Massive-Reddit-hack-litters-site-with-bizarre-pro-Trump-content.484484.0.html
Most likely Chinese hackers. They have been quite active recently specially with the COVID vaccine hacks.
I guess nothing to do with TikTok, because no mention of it in the posts made by them