Starlink definitively operates in Brazil as of right now, Internet service works (including ex-Twitter).
In theory Brazil could try to force SpaceX to stop by taking legal action through the US court system, or administrative action through the international bodies that coordinate satellite communications frequencies and orbits, but that would be unlikely to work.
Oh by the way, there seems there's going to be a very large fine for Brazilians circumventing the block to access ex-Twitter. So it may just be on the client side, if anything actually happens.