I have the Steam Ubuntu package (NOT the Flatpak) installed (so everything lives at ~/.steam/debian-installation, NOT ~/.local/share/Steam). When I install SteamCMD (from apt) and run the client, it fails to automatically find loginusers.vdf and libraryfolders.vdf. This issue occurs until I uninstall SteamCMD and manually remove the residual files left by SteamCMD in ~/.local/share/Steam (the package does not clean up after itself when removed for some reason).