By skyforbes 
Windows 10 unable to perform Windows Update with error “Your device is missing important security and quality fixes.”, after clicking on “Check for updates” button still showing “You’re not up to date” message with same error message.
Additionally, Windows 10 System Tray show Windows Update error icon with red exclamation mark as below.
Solution 1: Enable Windows Update Advanced Option
Step 1: Open Start > Settings > Update & Security.
Step 2: Click Advanced options link.
Step 3: Make sure Give me updates for other Microsoft products when I update Windows is checked.
Solution 2: Make sure Country or region setting is correct
Step 1: Open Start > Time & language > Region & language.