Fill Gaps in Palette Layout

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.

Thanks in advance for any help!

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

Could you provide an example of a custom layout that would achieve something similar as my desired behavior?

Not similar, but the basics of a layout that position the nodes based on each other are here:

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.