My palette is using the default layout and looks like the following when resized to show multiple columns:
As shown in the video, the layout is grid-like with each row of groups starting after the biggest group of the previous row, causing big gaps like between Source2/Source3 and the groups above. Is there a layout or layout property that could arrange the groups as shown but with no gaps? Meaning the groups would have a staggered layout to them.
There is no built-in layout that will do what you want. However, you could define your own layout that does this. In addition to all our complex custom layouts, we have a very basic example of a custom layout here: Extending GoJS -- Northwoods Software
This lays out the nodes only in the X direction. You have to decide where and when you want to wrap to get to the next column. You can pack them however you like, geometrically, though I think you might find more rules are needed as you develop it.