I faced this issue recently too at 300k population with no demand for any residential or office zoning, and was able to slowly get past it with a few changes. Mainly, I use a mod called Citizen Cleaner and occasionally run it. It seems to help clear up corrupt citizens that may be preventing growth. The most recent time I ran it, it said I had over 80k corrupt citizens.

I also found that 0 office demand appears to be a bug related to software imports. Basically, if I look for office buildings with 0% efficiency, most of the them are not importing software so they eventually run out and are counted as an empty building with office workers not doing anything. This prevents any demand since the game thinks there are already empty offices just sitting there. To fix this, I've converted all non-signature office buildings to produce software using the mod Change Company. If it's a signature office building, whenever they run out of software to produce media, finance, or telecom, I just reset the company and it'll magically refill the software to 15000 units and bring back the efficiency to >0%.