Is TikTok even search engine friendly? I don't remember ever ending up there by searching for something (that's not explicitly someone's TikTok account).
Surprisingly very search engine friendly. It only uses the titles and tags, though, I think.
pinterest has it's place. It's bad rep is because you have to be logged in to see anything.
You definitely don't need to be logged in. I used it in other browser sessions sometimes and you just have to scroll down about half a page and click "Explore" and it works fine.