I have installed the game through the Microsoft store with Game Pass.

My Windows is up to date. I've run the game in Admin mode.

I've tried creating the correct folders for save games based on the locations listed online.

Nothing has worked. Still can't save my game at all. No autosave, manual save stays grayed out (in or out of ship), no F5.

Is your Save Games folder being managed by some utility, like OneDrive or some other online sync/backup utility? I found that the entire folder would get botched completely if OneDrive was backing up that folder.

I don't think so, but I'll definitely check. I don't really use OneDrive, but it is usually running in the background because I've never bother to kill it as an auto-start program.