Outside websites(discord, etc) are used to coordinate brigading now, since the admin crackdowns.

I have also received sustained harassment over time from comments made on reddit. It's happened twice. I forget what I did to offend the one time, but the other was that I said someone should consider adding a content warning to their post because of something very unpleasant dropped out of nowhere near the end of it. Both times they followed me to other subs and would reply to my posts there, with stuff that was clearly off but not rule breaking. The reason I remember the one so well is that person was replying with the thing I'd said bothered me, no context just the words copy-pasted from their post. The reason I didn't block them was because it's not my first rodeo and I wanted to make sure it wasn't escalating without my knowledge(at the time the block tool only made their posts invisible to me, and allowed them to continue interacting with posts I'd made, so I wouldn't know if for example they doxed me).

I don't tiktok or twitter, but I've never had to deal with things like that on tumblr. 🤷‍♀️