Now I used 'ubuntu-drivers install' to install nvidia driver, it set 'on-demand' by default, but it won't work for 'External display mode', it works fine when I changed 'on-demand' to 'Perfomance' mode. Could you help check if it's the nvidia's bug. Thanks!
@Alberto,
Now I used 'ubuntu-drivers install' to install nvidia driver, it set 'on-demand' by default, but it won't work for 'External display mode', it works fine when I changed 'on-demand' to 'Perfomance' mode. Could you help check if it's the nvidia's bug. Thanks!