You are referring to some HUD functionality, allowing to search menu commands. Yes, this was build in in the Unity desktop, the Canonical developed desktop environment used in Ubuntu for many years. This was one of its prevalent innovative features. It was not by default Alt+F1, however (this is in many DE's reserved to summon the application menu - the Activities view in Gnome), but the right Alt key (which you could have changed).

However, it did not generally catch on. Add to this that modern trends are to abolish the traditional menu all together, that implementing this is different for different toolkits (GTK programs versus QT programs etc), and on modern Linux desktops. Therefore, it is still not a common concept and we are still supposed to visually scan menus and submenus to find the option we want.

The Unity desktop is still available as a community project, but its future remains uncertain. The much more alive Mate desktop on Ubuntu Mate, however, has adopted that HUD. It is not enabled by default, but you can activate it. It is based on the implemantation of Unity. Apparently, you could hack an implementation in the KDE desktop.

For Gimp, we are lucky. In one of the 2.10 versions, a menu search function was introduced, although it received very little publicity. Hit (in perfect Lotus 123 tradition) the / key, and start typing the keywords of the commands you want to find.