In fact, I'm not sure Manchester United can win a position in the Europa League zone this season, but they have a chance in another way and that is to win the Europa League this season. Manchester United can maximize that opportunity if they want to participate in the Europa League next season, but I also know that it is a very difficult mission for Amorim.
Manchester United qualifying for the Champions League this season is never ever going to happen. If that is going to happen, I think the only way to realistically have a chance for them is if they were to start a winning streak of like 7-8 games and I think everyone agrees that the chance is like 5% at best. Even then they might not be in the top 4 as the other teams have their own games too. As you mentioned, everyone else would have to lose while Manchester United wins it all.
Newcastle is 5th now, which gives them the qualification for the Europa League and while Manchester United didn't win the last four games and even lost three out of those last four games, Newcastle has a huge winning streak going on. It's like night and day if you compare those teams.
The focus should be to take away as much experience as possible and finally find a team that can consistently deliver good results, but too many points have been lost this season already. It would be a mystery if Manchester United ends up in the top 5 this season. As hard as it sounds, but they should rather make sure to keep the distance to the relegation zone instead of dreaming of the top ranks in the table.