Only today I found out where the collision setting is for the foliage tool. (Put a mesh into the foliage tool window, then click on the “i” button to “Show settings for placed instances,” then click on “Collision settings.”) But your choices are to make it either ignore collision or block actors, right? You can’t do this UDK | InteractiveFoliageActor with the foliage tool?
By the way, this has absolutely nothing to do with UE4-26, but apparently I can’t post a question now unless I tag a UE4 version.