Manchester United succeeded to sell a star player they no longer needed and released a little bit pressure on salary budget too. With no plan from Ruben Amorim for Antony, keeping him in the club, paying him salary are very unreasonable actions and no club want to do this if they can find an exit gate for the player. Both Antony and Manchester United actually had to step back a little to finish this transfer deal with Real Betis.
The club that brought Antony to the team must have had a lot of plans for Antony, that's why they spent a significant amount of money to bring Antony to their club and I have seen videos on social media where Antony was welcomed very well by the club's supporters. However, this is definitely a good decision for Manchester United, it was already understood that the manager did not have any plans for Antony this season, but the manager sold him to another club without causing financial damage to the club by paying him an unnecessary salary, which has certainly reduced the financial pressure on the club to some extent.
Now if the club thinks that they will bring a new player to the club to strengthen a specific position, it will be easier for the club to do so because Manchester United will not have to bear the additional salary to bring a new player.