Is Act 4 getting hard reset?
There are never ever hard resets. The only time we have had a hard reset was after beta and when the game was released.
But a basic rundown of how the resets work is between acts in the episode we will get a soft reset. Which does reset your mmr by a bit but it does not set ur mmr to a max rank such as diamond which it used to before.
But between episodes we get a harder reset. Maybe by 2 ranks at most but it depends on your placements. You still will be in the same general area though, but maybe you need to grind a little to get back.
There are no hard resets in valorant ranked though, it is a common misconception.
also btw there are only 3 acts in an episode, so I believe you are talking abt episode 4, but even then it's not a hard reset.