Of course I could eventually come to my own realization without TikTok. But TikTok accelerated this by about 3 years in my estimate. That is an immense amount of time and energy saved. I will explain how TikTok's dynamics differs from other social media sites, and how it uniquely helped me.
Twitter tries to algorithmically sort your feed, but some users (including myself) find it buries too many interesting posts, and use the old chronological feed. Twitter is sparing about showing users and posts you don't follow (except for retweets from your followed accounts, of course). This leads to accounts becoming "curators", who you follow because they retweet interesting content. This adds a nice human touch, but also limits discovery to other users' interests. Interactions are generally limited to retweets/quote-retweets, and comment treads, both of which rarely have a deep discussion because the UI isn't designed to promote it. Twitter has small sidebars to recommend other users to follow, but this is a very slow method to discover new content, and these sidebars are smaller or nonexistent on mobile clients. Tumblr is quite similar, so I group its community and discovery dynamics with Twitter.
Reddit is community-based. Subreddits are formed, users follow them, and posts are voted up and down. A subreddit can dominate its hobby, and there is no way to fine-tune the content you see. For example, I like seeing the deals in /r/frugalmalefashion but have no interest in the higher-priced designer shoes that can frontpage. This reduces the signal to noise ratio for my interests, and there isn't another active subreddit that would more closely match my tastes. The comment sections are the highlight of reddit, since discussions can go quite deep and low quality comments are downvoted out of view. Discovery is generally limited to commenters organically suggesting other subreddits, especially in mobile clients where there "isn't room" for algorithmic recommendations.
Facebook is quite different. Your friends feed is very broad-purpose, and groups are very specific. Groups are often smaller than comparable subreddits, and there will be less experts present in a discussion. This can hamper discussions on things like deal-hunting, where more frequent users can summarize community opinion or relay their deeper experiences. In other words, you have to do a lot more reading to find the information you want, giving Facebook a much worse signal-to-noise ratio. Comment sections can be more informative than Twitter but more shallow than Reddit, and communities are less interested in liking informative comments to bring them to the top to discussion threads. There is minimal algorithmic discovery, with only small recommendation sidebars.
Instagram is a mix of all these sites. You follow specific users like Twitter, but reposts are limited to the Stories feed, and are therefore deprioritized. So you generally follow each of these users for their original content (or occasionally curation, if they like to manually repost others' work on their feeds like a "meme page"). Comment sections can be lively but shallow, and I find discussions are generally superficial. There is an algorithmic discovery page that can find some good recommendations, but you browse it by thumbnail, limiting discovery.
YouTube is also interesting. You generally follow creators' channels like Instagram, and there is no easy way for "curators" to promote others' content without making a "meme compilation" video (and getting copyright strikes). Comment sections are second best to reddit, but not quite as good. Discussion is limited by the fact there has to be a relevant video for everyone to comment under - there's no way to make a quick post about a hobby without making an entire video, or making an oft-ignored text post. Discoverability is also very good, with the algorithmic feeds and recommendations being very accurate. But they lack variety and don't seem to try and dredge up old interests. When I watch a lot of automotive content for a week, I find recommendations about my other interests (like architecture) quickly disappear and only resurface for viral videos that don't align with my interests.
Finally, we have TikTok. You can follow creators and access a dedicated feed of their videos, but the primary method of consumption is the "for you page". There's some semi-scientific tests by users A/B testing videos (and comparing feeds to friends with similar interests) that lead to a general description of the FYP algorithm. The algorithm seems to form groups of users that like a particular cluster of videos/creators. Your new videos are shown to a few users in each of your clusters, and if some engage with your video, it is shown to more of that cluster and is tested against adjacent clusters. This significantly improves discoverability by letting obscure users' videos go viral, including one of my own quickly achieving 50k views (while all my other videos remain below 2k views). This is unique because it allows every hobby to have subcultures and nuance. I like car technology and engineering but not street racing or showy designs, and so I am clustered accordingly. It's obvious that there are racing and show-car clusters (some videos appeal to many clusters and the comment sections reflect that), but I am rarely shown that content.
This FYP algorithm can also help discovery about adjacent clusters. If you like videos about hikes, it will test videos about other activities like camping, and adjacent hobbies like environmentalism. This isn't hard coded - those are all just naturally occurring, adjacent clusters that each have overlap with hiking enthusiasts. So when I kept liking content about mental health condition "A", it because steady component of my FYP. Also interestingly, having a different condition "B" puts you at a 30% chance of having condition "A", despite the two having very separate communities on sites like reddit. So content from people with both condition "B" and "A" also appeared on my FYP, and I watched/liked the videos most relatable to me. As I began to see more content exclusively about condition "B" (and found some of it to be relatable), I began to consider if I also had that disorder. This wouldn't have been possible on other sites, since the subreddit for disorder "B" is quite heady and difficult to be easily introduced to. And I have a subtype of disorder "A" that is less common, so its community was less useful too. The communities on sites like YouTube or Twitter is so scattered to be practically useless.
Once I had a strong list of symptoms for each disorder, and some new vocabulary to help describe certain symptoms, I found a very qualified psychiatrist to evaluate me. The TikTok algorithm isn't perfect - I though I also had disorder "C", but after evaluation, it was determined that my symptoms don't match and may actually be from an unrelated issue.
No other social media app/site has the ability to navigate a large and varied community to find the parts that best fit each user. And no other social media app is as good at finding overlaps between communities and allows users to navigate them simply by interacting with content. For those reasons, TikTok is the best site for my browsing style, since I like to hop between communities and discover new ones that best suit me. It accelerated my exploration of existing thoughts and feelings so I could explore them to their fullest and see if each disorder's community matched my experiences, without requiring the effort of reading hundreds of posts and comment sections.