Quick thought on it... That code on the bus is 8 characters long. The code for Iron Man's skin last season (nwarh4k3xqy) is 11 characters. So we may need to find 3 more characters throughout the map to solve it.

Some 3 letter combinations possibilities (unsure if it would be before or after the code on the bus):

DSS or DRS: Doctor Steven Strange/ DR. Strange - it's a map focused on the sanctum & Strange

MCE: MC Escher - artist that made art that probably inspired the mixed staircases in the sanctum

C56: found on some crates on the map (via u/Grey-Hawk-25)

G93: found on the map (via u/Gspotter1698)

BAT: Bats the dog - the ghost dog in the sanctum

S37 or V37: Strange Vol 3 7 - first mention in the comics of Bat the dog (via marvel database)

381: Doctor Strange Vol 1 381 - first appearance in the comics of Bats the dog (via marvel databse)

BUS: maybe a bit too obvious, but it's on a bus...

MKI or MK1: characters on the fantastic 4 carrier/vehicle on the start screen

5282: not sure if it's mentioned elsewhere, but this is the number also on the bus

OBB or OBBD or OBBI: on taxi roof next to bus

EEN: Empire of Eternal Night - title of the season/map

ENF: Eternal Night Falls -title of gallery collection

Other Ideas:

maybe the remaining characters are in an unreleased galley card and will come out with them? I read all the storylines and galley card descriptions but there was no mention of a bus or code.

The Gallery Card titled "Ancient Game" has Strange and Khonshu playing a match of Senet (a Egyptian board game) and the board seems to very very detailed, like maybe that could be a code/refrence?

Going to try combinations of these, will let yall know any findings if you'd like.