@cabel I have the same problem with junk posts at #Threads as you do. Today I noticed something strange: I opened the profile of one of the hate spammers and saw that I *followed* that account. At first I was baffled as to how this could happen, but then it dawned on me: I'm used to tapping on the round profile picture to review or block the account. In the Threads app, this action isn’t "open profile", but "follow and open profile”.
I pretty much followed all the garbage accounts I inspected.