It seems that Joao Felix's return to Atletico Madrid did not make him Happy. It seems that he still can't get in touch with Diego Simeone. With these bad rumors, Joao Felix has been linked with many clubs wanting him. I think Joao Felix is a good player, at Chelsea he was not at his maximum because of the coach. There is news Barcelona and Man United are interested in Atletico's most expensive player. Of course they can take advantage of this bad moment to get Joao Felix.
Atletico Madrid is a club that to be used mainly for business, they're not want to achieve anything and only try to find a potential cheap player, then sell at high price. Barcelona don't have a good financial, it's impossible they would sign Joao Felix. I think he will join in one of EPL club again, maybe Newcastle United, Tottenham Hotspur, Manchester United, those clubs are have a high possibility.
I don't agree if you assume that Atletico Madrid don't want to get anything but a young player and then sell him when he's ready to be made into a star player. So far Atletico have been too economical to spend money in the transfer market, which has resulted in them having difficulty competing with Real Madrid and Barcelona. Business in football needs to be done to make a profit for the club, but trophies are far more important because the aim of competition is just to win trophies.