I find myself missing Unity all the time. It felt so much more polished than Gnome, particularly in the little things. I have basically switched to Elementary for my desktop Linux at this point because it feels like they’re the only ones actually trying.

Oh yes! Even more, the user interface was amazing. You could search the global menu ("HUD display") with just pressing the ALT key (similar as you can do on Mac OS X in the Help menu). This was incredibly useful for programs I rarely used but knew the name of the option I was looking for. I know the global menu was super hacky for basically any non-GTK/Qt application (such as Libre office). But it was space economical and still very functional. I never had such a desktop experience afterwards.

KDE has Alt-space for krunner. It can search and launch in many categories, from open windows to application names to e-mail addresses to settings modules. It can also calculate, run web searches, etc etc

Krunner is great (and similar to what you can do with the Gnome shell search or OS X spotlight), but it won't search the menu of your current application.

There are plenty of hints how to restore a Unity-like global menu feeling with Gnome, for instance https://www.linuxuprising.com/2018/05/how-to-add-global-menu... -- you can also get a global menu in KDE Plasma, it's called "Application Menu Bar" and seems to be included by default. I neither tested both of them.

Here is a GIF of a similar function: https://149366088.v2.pressablecdn.com/wp-content/uploads/201... -- the name of this tool seems to be Mate HUD, cf. https://github.com/ubuntu-mate/mate-hud