What i’ve see shows that Threads does have ongoing use. Meta has reported on earnings calls that there just under 100 million MAU.  Given there’s only 140 million accounts, that’s actually really impressive retention. I suspect the way they’re cross promoting threads posts which you can only read fully by clicking over to threads from Instagram is a lot of what’s propping up the numbers.

https://explodingtopics.com/blog/threads-users