As you can see from the heated debate, the real answer is he can live almost anywhere and people DO make all kinds of different living choices in NYC based on their personal priorities and financial situations.
I have lived on the UES in the same neighborhood I moved to when I graduated from college in the early 2000s. Over the years I have worked in the financial district, midtown east, midtown west, Jersey City, Times Square, Westchester and even Stamford, CT (all via public transit, I have never had a car here). I originally chose my neighborhood because many of my college friends lived there at the time.
I work at a major bank and my analysts, who are right out of college/early in their career, live in all the neighborhoods suggested throughout this thread. Almost all the folks who graduated last summer have continued to live with their parents (from many different US states) until the dust settles post Covid.
Personally, I prefer Manhattan, but there are vibrant communities and easy commuting access via the Path to Jersey as well as LIRR to Long Island and MetroNorth to CT. Unless folks have family in Long Island/CT/Westchester, it's rarer to see recent college graduates chosen to live there, but it certainly happens. Hoboken and Jersey City are more common choices outside the city boroughs. FiDi can be very quiet after working hours, and I prefer to have separation from my office, so that wouldn't be my personal first Manhattan choice, but YMMV.
My practical suggestion is he poke around StreetEasy.com - that's the best source of NYC apartment information right now (renting or buying!) and can give him good info on what he can get in each neighborhood for his money. Finally, there are a lot of sublets available right now, or opportunities to take over leases at a discount or X months free rent. I just negotiated with my own landlord for a significant annual reduction.
Finally, my bank is still primarily in WFH mode, and anticipate it will remain that way until Labor Day. Many firms will consolidate real estate and have folks desk share so they will come in some days vs. all days. Our CEO had been very strong in saying we would return in full force to office, but this position has been softening. Future WFH abilities will vary by function/firm but is good to understand as it may mean he does not need to rush into finding an apartment immediately and could explore different neighborhoods while subletting or taking shorter trips in.
Good luck! It's an exciting transition