Deleting C:\Program Files (x86)\Steam\appcache\appinfo.vdf and restarting Steam seems to have worked. Perhaps the FAF Uninstaller can detect if Steam is open and suggest that the user closes it before proceeding.
Im not sure if it’s FAF related? Maybe you deleted your supcom files as well? Don’t know how FAF would break steam, has never done it for me in 2 years