If you have installed the latest Stand-Alone Addon Manager for FS9, and still doesn't work, I'm afraid you don't have any other options than rollback the latest Windows update.
The issue is, nobody at FSDT still use FS9 or has FS9 installed anymore, since we stopped supporting it in 2011 ( 7 years ago ), it's nice the software worked so far in Windows 10, but we cannot possibly still support it with every future OS release anymore.
I cannot even install Visual Studio 2003 on Windows 10 (starting from build 1703), so I can't even load the source code of the FS9 software, and I don't even have any PC left with a DVD reader to install FS9 itself.
*Maybe* you could try Virtualization, and run FS9 under a virtualized Windows 7, using Microsoft's own Hyper-V, Oracle's Virtual Box and WMWare Workstation Player.