FSX:SE doesn't require any Compatibility setting to work under Windows 10. Nobody use it that way, and that's not how Steam install it by default. The only setting which is not default, is run As Admin, which is not a problem for us.
Maybe you have a 3rd party addon that requires it, because it has been programmed without respecting MS UAC directives (which were in place since 2006 Windows Vista) and, because of this addon, you are forced to run FSX in XP Compatibility mode, which will also reduce performances, since it will force video drivers to run in a lesser mode (WDDM 1.0 vs 1.1) and it will have the OS redirecting all file access and registry calls. So, XP Compatibilty is bad and shouldn't be used.
Our software, instead, it's 100% fully compliant with UAC, so it won't work under XP mode.