Jay is correct. When the icon is green and you open the Windows Defender Security Center and select "Device Performance & Health" it will show the date of the last scan under "Health Report". Each of Windows Update, Storage Capacity, Device Drivers and Battery life will list "no issues". In the case where there is a red check on the icon, the option to run the Troubleshooter will be available for the item under "Health Report" where an issue is seen.
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Take a walk through the
"Security Garden" -- Where Everything is Coming up
Roses!
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