Kickoff currently features categories in the same vertical style as vertical tabs in Edge/Firefox, and a UX thing that I noticed from Edge that might be beneficial would be the ability to collapse the text to just square icons, giving users more space for their apps and less visual noise. Edge implements their vertical tabs sidebar with a pin button to keep the sidebar non-collapsed, but I think for KDE it would be better to just have open/close sidebar arrows. It would be akin to the collapsing the sidebar in Audiotube I guess?
Another idea I had would be the option to replace the categories with letters, so that you would click a letter and it would bring you to that letter’s apps. That would probably require 2 columns or more to make it convenient, though. Alternatively, being able to change the default view from favorites to the All Applications view would solve problems. Legacy Kickoff had the ability to change the default view.