Windows System File Checker tool, commonly known as SFC, has a /scannow argument that will check the integrity of all protected Winodws system files and repair any issues that are found. Starting today, Windows 10 users are finding that the /sfc scannow feature is no longer working and that it states it found, but could not fix, corrupted Windows Defender PowerShell files. Microsoft released a support bulletin explaining that this was caused by a out-of-band update that is causing hash mismatches.
Source: https://www.bleepingcomputer.com/news/microsoft/windows-10-sfc-scannow-cant-fix-corrupted-files-after-update/