Newcastle still don't have a world team, but they are good enough to finish in the second tier of England. They won't be 3rd this season, but I don't think that's the goal either. They just want to finish with the best 6-7 and then hope that they can bring in some reinforcements again next season. They have so much money, they can pay every player in the world and they can pay all the salaries as well. Mbappe wouldn't be a problem either, but the problem with very good players and stars is that they have little interest in playing for Newcastle United. Of course, PSG and City also started this way.
If Newcastle manage to finish the league among the top 4 teams this year, they may be able to attract the attention of high-profile players next year. For example, if they had played in the Champions League this year, they might have caught the attention of Cristiano Ronaldo. I think Mbappe will not be a difficult transfer for them. Mbappe's interest in money is also a known fact. If Newcastle make a good offer for him and they manage to qualify for the Champions League this year, they can sign Mbappe in my opinion. Also, it might be easier for Mbappe to change his mind if they sign up for a few more star players before they make a transfer offer to Mbappe.