I'm looking at a default Defender configuration in Server 2016. I'm not sure how to discover what these '0' mean for the ThreatDefaultAction:
HighThreatDefaultAction : 0
LowThreatDefaultAction : 0
MAPSReporting : 2
ModerateThreatDefaultAction : 0
I would think from the Set-MpPreference documentation that it's Quarantine, but that same bit of text references a Parameter set that starts with 'Clean', not 'Quarantine'. This explanation of ThreatIdDefaultActions doesn't even have a 0 in it's list: Add-MpPreference