I still think your biggest problem is the lack of a top class out and out striker.
Martial is a decent inside forward & Rashford has bags of potential but neither seem to have the killer instinct to sniff out tap ins in & around the 6 yard box and you wouldn't put money on either to convert in a 1on1 situation.
Going back through the years you've had Ibra, Van Persie, Berbatov, Van Nistelrooy etc. guys who will get you 20 - 30 goals a season just on instinct and who will get the best of out the creativity of players like Fernandes (who looks an outstanding buy btw).
Appreciate they are remarkably difficult to find and cost big money but got to be a priority in the summer, if you can afford one given your bloated wage bill which won't be helped by the return of Alexis Sanchez after a shocking spell in Italy and you'll do well to offload him with his outrageous contract!
Going through the team I do think you still have a great squad with bags of potential:
De Gea - world class
Mcguire - champions league lvl centre half & will prove to be a great acquisition
Lindelof - looks a lot better alongside Mcguire, United's 2nd best centre half
Smalling - good defender but poor distribution, that said is probably the 3rd best DC at united (better than Jones, Bailly, Rojo)
Shaw - will never be a world beater but steady away and better than the media perception (his stats back this up)
Wan-Bissaka - big potential, very good defensively, needs to improve going forwards to be an attacking threat but surely Englands 2nd best right back after TAA
Dalot - young, not seen enough of him
Williams - another youngster, works hard and is quick, lot to learn defensively but has potential
Fernandes - already looks like your best player, hopefully proves to be consistent
Pogba - divides opinion but has the ability to win games single handedly. I really hope he stays and proves the doubters wrong. Do think his attitude / mindset needs to change for him to achieve his massive potential
Fred - has improved recently but still not convinced he's anything better than a squad player
McTominay - dependable & high work rate, decent squad player and still young
Perreira - doesn't look anywhere near good enough to be a united player for me, cash him in
James - fantastic first half of the season, great pace & work rate, great signing
Greenwood - bags of potential
Martial - not consistent enough for me - not enough goals or assists to ever be a top top player but decent impact sub
Rashford - has all of the attributes to be a world class player, again just needs to work on finishing & decision making in the final third but plenty of time to develop
Surplus to requirements:
Sanchez
Mata
Matic
Jones
Bailly
Rojo
Lingaard
If Man U can get rid of the above, who should they try to bring in?
1) World class striker. Haaland? Still early days but he does look the real deal & has history with Solskjaer plus is young & has a sensible release clause.
2) Top centre back. Mcguire, Lindelof +1
3) Creative wide player - Sancho? Not an inside forward like Rashford/Martial but an actual wide midfielder / winger who can pick the ball up out wide in midfield and create chances.
Thoughts?