In Service Activity OnPremise, there was a Form Assistant when you create an activity, showing you filtered Resources that could be selected for a selected Service based on rules. Ie.: Choose 1 from this group of resources, then choose 1 from another group, and so on.

But on Cloud this Assistant it is not showing up. Microsoft support says "This feature is not available on cloud instance for now. We have determined that we have ran into a product limitation and have no workaround at this time"