I’m using WSUS, but find that Windows Defender definitions are not updating. To fix this and update Windows Defender definitions through WSUS, you have to log onto WSUS, go to Options -> Synchronization Options -> Products and Classifications and tick the Windows Defender tick box.
Once this is checked you will be able to download Windows Defender updates, but you still need to check that Definition Updates is ticked under Update Classifications.
If this isn’t ticked, WSUS will not download Windows Defender updates and you won’t be able to update Windows Defender through WSUS.
Once WSUS has done a synchronization to download the new updates, clients will then be able to download definitions from WSUS.