A repeating group, for definition supposed to be everything equal. But if you don’t want to show something at element have the option to be visible or invisible. You have to add a condition for show the button just for the firt element, at this case.
I had this challenge as well. The best turnaround I found is the following.
I used the repeating group from Group 2 and Group 3 only and used the “:items from #2” option at the end of my dynamic expression (list) in the data source.
Above the repeating group, I created:
a standalone group for the “+” group
a standalone group for the item #1 (your Group 1). In the Source of that group I used the same expression as the repeating group and ended it with “:first item”.
I’ve achieved this by automatically creating a new thing in this group’s data source with a unique name, say, “emptycellnewbutton”. Then you have to:
Data source is first, just the data that contains “emptycellnewbutton” merged with the rest of the data.
It this cell contains name “emptycellnewbutton” then make 1. cell’s content invisible, and this + button visible.
This will ensure that your button is always first, and the rest of the data second.