From what I'm seeing, it seems to me that Antony had some kind of problem with the Manchester United coach. At Manchester United, when a player disagrees with the coach about something, then that player's career is destroyed in the team and the club's management does not intervene in favor of the player.
Looking at the statements made by Antony's agent
Antony’s agent Pedroso: “We respect the opinion of coach Ruben Amorim, but we completely disagree with his analysis”.
“To attribute Antony's lack of success at United solely to physicality is a very superficial argument and does not reflect reality”, told Marca.
https://x.com/FabrizioRomano/status/1897279087972139300It seems that Antony had personal problems with the Manchester United coach, Antony probably disagreed with something the coach did and the coach didn't like it.
Whatever the issue might be regarding Anthony’s departure and what has been said by his agent seems to be proving valid because of Anthony’s recent form since his loan move to Real Betis. His form has been unarguably outstanding even when he played against Real Madrid he completed a 7.7 match rating which is rarely something we see in the Premier League.