You want to differentiate between 5xx and 4xx errors?
Drill down to the Error Dashlet, there are different error Rules for 4xx and 5xx there so you see them seperated. You could also create more specific error rules if you want.
Oh you mentioned appmon in your title so I though you are talking about that.
In Dynatrace you can filter for either 4xx, 5xx or a specific response code: