I don't think I mentioned "KDE app" or games? KDE's Global Menu works with apps built with other toolkits than QT, and games are typically not considered apps. It would be cool if games did something similar though, I would love to be able to go into a games options and type "subtitles" to quickly find the option.
But either way, I still disagree with your comment that "all GUI apps on macOS and KDE (Wayland) have searchable menus", because this requires a menu system that is exported via a specific DBus protocol (https://stackoverflow.com/questions/75215820/how-to-implemen...), meaning it requires support from the application itself (possibly via some toolkit it uses), which IMO is demonstrably not "all apps".
On macOS and KDE (Wayland), they do! Agreed it's really handy.