I am using FSX-Steam and Windows 10.
According to WIN10, the following FSDT airports are installed. The first 3 have been purchased. KORD has not (yet)
KCLT (1.0.2)
KDFW (2.3.1)
KSDF (1.0.0)
KORD (2.5.0.3)
According to the Addon Manager (4.0.0.

,
KCLT Active and Installed
KDFW Active but not installed to the Scenery Library
KSDF Active but not installed to the Scenery Library
KORD Not installed to the Scenery Library
On the FSX Settings Scenery Library under the Scenery area list, only FsDreamTeam KCLT appears, and apparently is the only one of the four functioning.
Clearly FSDT scenery can work on my system, but I must be doing something wrong, probably with the installation.
I noticed that when I installed KORD today, there were two options pre-selected, one of which said something about FSX-Steam standalone. Anyway, I left both selections checked and proceeded with the install.
Any suggestions?
Thank you