In the latest graph api microsoft has not provided a way to download or access attachment from list items..
so the limitation is there in the UiPath activities as well as they use graph api in the backend
for now if you need it few ways
Instead of attaching in list item change the list to have the file url and upload file to any drive so that the files can be access via download or get files activities
If 1 is not feasible then you might need to use old rest apis to get the items..but again for this the whole code needs to be written by you..Sample reference is attached