I am trying to upgrade my macbook air. Already ok but I stuck here. Can input password now or can't skip this option also. If I want to restart now also can't. What to do now? If I force restart should I download the Mac OS again?
Not sure I understand what you mean about losing data. Which macOS version are you upgrading from and to? I'd try a force restart and then evaluate. If you end up back on the Apple ID log in screen and are still unable to log in, you may need to contact Apple Support.