Zardnaar
Legend
I assume mass transportation is via Teleportation Circle.
The reliance on Renaissance Era methods is only relevant for the sake of "flavor".
More pragmatically, magitech can feel like modern technology. The Eberron setting makes magitech function as if the 1900s. In the Forgotten Realms, certain cities function this way.
If 10% of the population are mages, that would be more than enough. Especially if they are high level.
FRs not magitech and 10% are not mages.
Don't get me wrong I'm not opposed to s fantasy city having two million people but they woukd need a very good setup to make it work.
Sharn with a lightning rail, airships, magitech. Population 200k.
More information needed but 5E Waterdeep map very similar in size to 3.5 one.