Thanks. Please also send the output of
update-alternatives --display glx update-alternatives --display nvidiaDo you know why you have libnvidia-cfg1 (from the current, not the legacy driver)installed? That probably stems from the attempt to install nvidia-settings for the current driver.
(You also have libnvidia-legacy-390xx-cfg1 installed.) If you uninstall libnvidia-cfg1 everything should be back to normal again. Andreas