Now you would create your first dropdown control, and for the Items property, you would use the formula Distinct(Impacts, Title) to only show Cost, Program Impact, and Schedule in the dropdown. Then you would add a second dropdown and set the Items property to Filter(Impacts, in SCategory) where ddSelectType is the name of the first dropdown box. Just like that you have cascading dropdowns. For more information check out this post from the PowerApps team SharePoint: Cascading Dropdowns in 4 Easy Steps! or this community video and don't worry, you can do it just as easy without SharePoint.