ubuntu 18.04 nvidia-driver-435 E: Unable to correct problems, you have held broken packages.

這是因為顯卡驅動沒有清除乾淨，所以如果要用sudo ubuntu-drivers autoinstall安裝顯卡驅動之前要在終端機先執行以下指令

$ sudo apt remove --purge nvidia*



參考
https://ubuntuforums.org/showthread.php?t=2417585