Hi,
I'm also experiencing this problem. I uninstalled (to update to v7.0.4) but it is now giving this error - it actually says "Error loading EXE.xml" the installer then quits within about a second, it's not possible to click next or anything similar, and it doesn't seem to generate an install log file either.
When I looked in the specificed location for the EXE.xml (I'm a MS Store install user) there wasn't a file there - and I've now created a blank one from a template, but it's still giving the same error.
I have successfully installed by unchecking the start with exe.xml option, but something weird is occuring here I think? (and FSUIPC is not accessible once MSFS is running, and yes, I have waited 120 seconds)