I don't have this active in a lab for testing.
Would it not be sufficient just to query for status other than NotStarted o Completed?
I would do something like (Just an untested sample) if you need to correlate:
let NotStarted = UpdateRunProgress
| where InstallationStatus == "NotStarted"
| summarize arg_max(TimeGenerated, *) by Computer ;
let Status = UpdateRunProgress
| where InstallationStatus != "NotStarted"
| summarize arg_max(TimeGenerated, *) by Computer ;
NotStarted
| join (Status ) on Computer
| where InstallationStatus_1 != "Successded"