How do I get the virtual keyboard to work in SDDM?

I've installed Kubuntu (26.04 LTS) on a laptop with a touchscreen. When logging in, there is a button for the virtual keyboard in the lock screen, but it does nothing, nor does tapping on the password field. Once I've logged in, it works fine (including on the lock screen), but once I've logged out it breaks again. I also tried the Silent theme, which has a different on-screen keyboard, but that also didn't work (it shows up, but the keys do nothing). How do I fix this?