Threads on Twitter are usually not a very compelling source, I am not against changing my opinion if the evidence is compelling, but that was not it.

See for example how the question is answered over on r/askhistorians:

https://www.reddit.com/r/AskHistorians/comments/140daad/how_many_people_died_during_the_tiananmen_square/jmw0ns0/

Well sourced with actual recent publications and honest as to what the uncertainties are.