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