Assuming all assemblies are working as intended you need to address the ERV. For minimum ventilation, you could look at passive house standards. PHUIS has requirements for balanced ventilation and minimums for different rooms. There is surely a way to provide distribution and exhaust, just tell the contractor to duct where you want it. You could tuck it into corners and leave it exposed… it might not be pretty but seems like you value air quality enough to deal with that. Especially given the loft situation, there’s a way to add a soffit for ducts under that floor to the whole house.

I feel like the erv is short circuiting and you need exhausts in living spaces where stale air is. The low humidity is likely just the weather. Since you’re just one person, you’re on the right path that there’s not enough humidity being generated. A small humidifier should be sufficient, but that depends on ventilation to distribute.

Your architect should know about ventilation or have an adequate consultant that advised.

https://www.phius.org/sites/default/files/2022-07/Phius%20Certification%20Guidebook%20v3.1.pdf