The post Zone Areas: Measured vs. Calculated (October 2017) helped me find an acceptable solution.
I recently finished my model with complex wall profile for the eave and it affected all of my area and volume calculations by adding black anchors to my zones.
In my case, however, I cannot lower the zone height below the eave profile because I need an accurate volume for our local codes, which have bulk volume restrictions. I am also unwilling to change my exterior walls to "No Effect on Zones" because I need the boundaries for rooms.
My solution was to move the zones off the walls and site. The updated zones are now accurate. It's an extra step or two, but much better than manually calculating each zone and importing a spreadsheet.
It seems that Archicad should address this. The zones I placed are all manual and should not be affected by any walls or aberrant complex profiles.
Archicad 26 Macbook Pro, Ventura 13.6.3