Hi Dontask,
Is your PC connected to the Internet and the drive has 150 GB space?
says
To install Microsoft Flight Simulator to a different folder, click "Browse" and select a new destination folder if you have created one already or create a new folder before saving that new path.
*The drive selected for installation must have at least 150 GB of free space available*
MSFS wanted to default install to /......myname/appdata/..../ for some strange reason when I installed it. Most people would not catch this during install while clicking "next" without reading. If the /view/Hidden Items/ checkbox is not checked in explorer, the sim will not see the install files the second time it starts. The install location should be changed in MSFS settings. Why the default install location is the $120 question.