Windows Defender reports error 0x800b0100

On startup, Windows 10 pops up the following alert:

An error has occurred in the program during initialization. If this problem continues, please contact your system administrator.

Error code: 0x800b0100

Windows is up to date and I've done my research, but sfc /scannow and dism /Online /Cleanup-Image /ScanHealth didn't fix the problem - the former just reported that there were corrupted files, not how to restore them (the resulting CBS.log is several megabytes in size and not very helpful either).

The same error pops up whenever I try to access Windows Defender via the start menu - however, both services.msc and the Windows Defender section within Windows Settings report that the respective services are active.

a) Can I safely assume that the machine is properly protected?

b) How can I get rid of this annoying dialog?

I'd very much appreciate any help.

It is recommended you to fix this problem, instead of ignoring it. Try below suggestions.

Re-start system in Clean Boot - Perform a clean startup to determine whether background programs are interfering with your game or program: https://support.microsoft.com/en-us/help/331796/perform-a-clean-startup-to-determine-whether-background-programs-are-i

>the former just reported that there were corrupted files

If both SFC and DISM.EXE reports error about system files. If there is system backup available, just restore system back to previous working state.

Besides, you can try - How to: Perform a Repair Upgrade Using the Windows 10 ISO file Important thread: https://answers.microsoft.com/en-us/windows/forum/windows_10-windows_install-winpc/how-to-perform-a-repair-upgrade-using-the-windows/35160fbe-9352-4e70-9887-f40096ec3085