Isak wants to leave Newcastle United and finds a new challenge and chapter for his career but surely he will look at a better club than Newcastle United. He will not have interests of joining Manchester United and remember that he is on transfer list of Liverpool. I believe between Liverpool and Manchester United, he will choose Liverpool and this club already sold Darwin Nunez to Al Hilal after buying Ekitike and perhaps they are preparing another slot for Isak.
Isak has not yet made any official statement about leaving Newcastle. We have not even seen any such gossip yet. Liverpool made an offer to buy Isak for 110 million. But Newcastle management rejected it. And Newcastle management does not want to let Isak go now. But Isak has not said anything about his desire so far. However if Isak wants to leave Newcastle, Liverpool may be the best option for him. Liverpool's squad is very strong this season. With Isak's help, liverpool may be able to dominate both the Premier league and the Champions league.