The TitleBar Button sets are just folders with PNG files in the following folder: C:\Program Files (x86)\DisplayFusion\TitleBarButtons\Buttons. You can add custom icons to one of the existing folders, or you can create your own folder for custom ones :)
Glad to hear you like the window picker as well, it was a great idea!
Which always on top bug? The Windows 10 one that occurs when the taskbars are on the side?

Kevin F.
456 discussion posts
Not sure, but it was stickied here :"Windows not coming to front when clicked (this is a Windows 10 bug triggered by any program that uses TOPMOST on its windows). Workaround: Enable the "SetWindowPos: Disallow TopMost Calls" option in Settings > Advanced Settings."
https://www.displayfusion.com/Discussions/View/windows-10-known-issues/?ID=e71e1f5e-9e07-4f7d-b179-22253db2c30f
That bug :)
I know it says its technically win10, but lets be real, the issue resolves if you cut off DF, yall can fix this :)
I set the advanced option which made (most of?) the always on top button not work which is annoying in its own right, I set always on top through that proggram's setttings but it would be nice to use the titlebar buttons again.