I've been wondering the same. I believe the lore says that the highest floors in mallplexes are where some city services (security, health, transportation, and such) can be found. They're probably pretty much the same in 2077's megabuildings.
Gameplay-wise, that's where V would probably go to visit clinics, banks and police departments.
In Night City, in 2020, there is a City Hall, Justice building, etc, all at the City Center area of downtown, west of the mallplex.
New Harbour Mallplex houses 5,000 people and of course many many many shops. Admin for NHM is a separate building. Mall Security and Management (complaints) is on the top floor of NHM. "all complaints in writing, please."
A sample from Night City sourcebook, available at
https://www.drivethrurpg.com/product/589/Night-City
"Skinlight ... When want to be the light in his dark
future! " A high level cosmetic body shop, Skinlight
features the latest in light tatoos, including Image
Fashionware's Bodyline styles."
"SoSushiMe is the product of two lawyers in the early
twenty-first centurywho came up with the idea of marketing
prepackaged sushi in seaweed cartons to save unnecessary
waste. Now, with over 2000 locations in existence, this
franchise has become one of the most popular eating
establishments in the corporate world."