I have fsx and windows 7.
From the System requirements on the GSX Product Page:
http://fsdreamteam.com/products_gsx.htmlWindows 8.1 is the minimum supported OS.
As you surely must know, normal Windows 7 support ended in January 2015 and, 5 years later, even the Extended support ended on January 2020. Which means, Windows 7 is now almost 2 years outside ANY kind of support from Microsoft.
This means, that any time we update the program to support current OS, which requires compiling the software using updated MS compilers and libraries, it's very likely it won't work anymore on legacy OS, which are now completely out of support from Microsoft.
There's just nothing we can do about it, and this won't change in the future. If anything, it will be worse so, I guess sometimes even Windows 8 support will drop, and Windows 10 will be the minimum supported OS.