Acceptable Furnace Install in Sealed (foamed) attic

It doesn’t.

What is wrong with that amount of moisture in the attic?
It does nothing to a house that does not have a sealed attic.

A sealed attic is no different than a room in the house without a heat/cooling register (bathrooms, walk-in closets…). It is a buffered space that is insulated from the exterior and there is nothing in the space that will be below the dew point.

A sealed attic is an indirectly heated or cooled space.
The roof is insulated, just as the ceiling in a conventional home (only better, no wiring, plumbing, fire suppression, or vent penetrations).

If you have excessive moisture in the house, you will have excessive moisture in the attic.

You will have excessive moisture in the attic in a conventional home because the ventilation is not designed for the excessive moisture which is outside the design parameters anyway.

I may not be following you …

I think I understand. You just got to watch how much moisture is entered into the living area with a sealed attic than a vented attic, due to the natural water evaporation that occurs.