When I log in to my KDE session, I can’t just start typing my password. I have to hit a key or backspace first. How can this be fixed? Is it KDE upstream or what? I’d like to pursue this issue, so where is the upstream dev?
Maybe you could give people a bit more information. What kind of Keyboard? What is its connectivity? when did the problem start? your using sddm correct?
If this is specific to KDE, you might get additional help on the KDE Forums.
Or you could search/report bugs on the KDE Bugtracking System.