San Francisco is one of the most humid cities in the US (so much that mold can be a problem in some cases). Relative humidity is on average higher than Wash DC --but lower than Port Arthur, TX.
Yes, but its neither particularly hot (so it doesn't tend to be muggy), nor particularly cold (its cold for the densely populated parts of California, but that's not saying much), so the humidity isn't much of a problem.
Hence one of the reasons it waa attractive before it was a center of the tech industry.
To that point though, most of the neighborhoods I have lived in have had little to no fog. Russian Hill being the exception. I’m not sure how much of a difference that makes in indoor relative humidity or chance of mold.
The AC is appreciated, but you get acclimated to the heat. And anecdata of one, but I really miss the heat / humidity.
Texas civilization does predate AC after all for at least a couple centuries ;)
I've lived in Louisiana, Mississippi, and Georgia and mold has never not been a problem in those states. I have never lived in San Francisco though so I can't compare.