DeviceTvmSoftwareInventory
| where SoftwareVendor has "microsoft" and SoftwareName has "defender_for_endpoint"
| extend MajorVersion = toint(split(SoftwareVersion, '.')[0])
| extend MinorVersion = toint(split(SoftwareVersion, '.')[1])
| where MajorVersion == 10
| where MinorVersion < 8700
| sort by SoftwareVersion

You can use the Advanced Hunting Query to find out of date clients

you can find your version here https://security.microsoft.com/vulnerability-management-inventories/applications/microsoft-_-defender_for_endpoint/Versions