I think the Liverpool interest is genuine, but if Benfica play hard-ball or a bidding war breaks out I'd imagine Liverpool might pivot to options #2 or #3.
Man Utd are in a strange/awful position in the final third.
Cavani is gone.
Martial is a busted flush, but has 2 years to run on this contract.
Greenwood future on & off the field in huge doubt.
Ronaldo unlikely to stay beyond summer 2023.
Rashford needs a reboot.
Elanga looks worthy of some minutes - but IMHO as a 4th or 5th choice for a side with CL qualification ambitions
Shoretire & Garnacho have promise, but statistically unlikely to ever become regular first-team players.
Then for wide attackers there's only Sancho of note. The bones of £40m spent on Amad and Pellistri look unlikely to bear fruit.
If you take a pessimistic view on those in red above, depending on formation/style you could argue that Utd need 4-5 quality attacking players to come in across the next 3 windows (summer/winter/summer) and perform well.
That will be very hard to achieve.