Give me an example. Any example beyond this Space one we’re discussing; because I don’t know of any.
Basically anything that requires text input from OS-native text input fields to IDEs, word processors, spreadsheets, web browsers, terminal emulators and so on and so forth.
(I confess I’m getting frustrated at the ridiculously large fraction of messages in this thread that have somehow completely misunderstood things.)
In answer to your question: I’ve only really used keyup for either one time events (like keyboard shortcuts for UI elements) and for ending the status of repeated events (eg movement in games, dragging UI elements, etc).
I think if you were to search for key up events in GitHub, most of references might likely be games and other visual interactions rather than text entry.
But for reference browsers fire the keypress event on keyup